I concur in the affirmance of the judgment as to guilt and special circumstances, but I dissent from the affirmance of the judgment as to penalty.
In my view, the trial court erred when it permitted the prosecutor, over defense objection, to ask defendant what punishment would be just for his capital crimes. The question called for an opinion on the ultimate issue *733before the jury at the penalty phase, an issue on which defendant’s personal opinion could have no conceivable bearing.
The error was prejudicial. Defendant’s admission that death was the just punishment for his crimes—an admission that must have electrified the courtroom—seriously undermined the defense case for the alternative penalty verdict of life imprisonment without possibility of parole. Because the balance of aggravating and mitigating circumstances was fairly debatable in this case, there is a reasonable possibility that the error affected the penalty verdict. I would therefore set aside the judgment of death and remand the matter for a limited new trial on the issue of penalty.
I
Defendant testified in his own behalf at the penalty phase. At the conclusion of the direct examination, defendant accepted his counsel’s invitation to make a statement to the jury in mitigation.
Defendant told the jurors he was not the same person he had been when he was arrested or when he had killed the Shaffers. Defendant had recently begun to read the Bible, he said, and to “accept Jesus Christ as being real.” As a result of this religious experience, and as a result also of realizing “the value of the human lives” he had “stolen,” defendant’s “attitudes” and “personality in general” had undergone “noticeable changes.” Defendant said he had tried to be sincere and truthful in his testimony and had tried “to find some way to explain or apologize to the Shaffer family for the misery and anguish” they had experienced because of his “lack of respect for human life and [the] rights of all people.”
Addressing the jury, defendant concluded with these words: “I’m not asking any favors of you except fair judgment. I just want to thank you all for the sacrifices you have made to be here and to judge this case.”
Near the beginning of the prosecutor’s cross-examination, the following exchanges occurred:
“Q. Have you learned now that the Bible tells you to live by the law of the land?
“A. Yes, sir.
“Q. And that you’re responsible for your own acts?
“A. Yes, sir.
*734“Q. And that you are subject to the law and have to take the punishment that’s prescribed by the law?
“A. Yes, sir.
“Q. And as such what do you think your just punishment should be here?
“Mr. McClure [defense counsel]: I object. That’s not relevant, your honor.
“The Court: Overruled.
“Mr. McClure: As to what he thinks.
“The Court: Overruled.
“The Witness: If I were one of the 12 jurors, I would vote for the death penalty.”
Thus, after eliciting defendant’s admission that he was “subject to the law and [would] have to take the punishment that’s prescribed by the law,” the prosecutor asked for defendant’s opinion “as such” concerning the just punishment in this case. Because the jury had convicted defendant of two first degree murders with special circumstances, and because the law prescribes only two possible punishments for these crimes—death and imprisonment for life without possibility of parole—the prosecutor’s question called for defendant’s opinion as to which of these penalties would be his “just punishment.” Thus, the question effectively made defendant a juror in his own trial, forcing him to decide the ultimate issue of penalty. That defendant so understood the question is shown by his answer: “If I were one of the 12 jurors, I would vote for the death penalty.”
A defendant’s opinion about the just punishment for his or her own crimes has no relevance to the issue the jury must decide at the penalty phase of a capital prosecution. Penal Code section 190.3 lists the factors that the jury may consider in determining the punishment for capital murder. Most of these factors relate directly to the charges that resulted in guilty verdicts and true findings at the guilt phase of the trial. For instance, the jury is directed to consider at the penalty phase the circumstances of these crimes and the related special circumstances (factor (a)), together with specific aspects of the defendant’s mental condition during the commission of these criminal *735acts (factors (d) [extreme mental or emotional disturbance], (f) [reasonable belief in moral justification], (g) [extreme duress or substantial domination by another], & (h) [impairment caused by mental disease, defect, or intoxication]), and the defendant’s age (factor (i)) at the time of the crimes.
In addition to the Penal Code section 190.3 factors relating to the capital crimes, the jury is to consider any other criminal activity by the defendant involving actual or threatened violence (factor (b)), prior felony convictions (factor (c)), and “[a]ny other circumstance which extenuates the gravity of the crime even though it is not a legal excuse for the crime” (factor (k)). This last factor includes any aspect of the defendant’s character or record on which the defendant seeks to rely in mitigation. (People v. Boyd (1985) 38 Cal.3d 762, 775 [215 Cal.Rptr. 1, 700 P.2d 782].)
Appearing nowhere on Penal Code section 190.3’s list of penalty factors, a defendant’s opinion as to the just punishment for his or her own capital crimes cannot in itself be a circumstance either in aggravation or mitigation. The majority effectively concedes this by stating that in a capital case the defendant’s opinion regarding the appropriate penalty “usually would be irrelevant to the jury’s penalty decision.” (Maj. opn., ante, p. 715.) Thus, defendant’s penalty opinion could lawfully play no direct role in the jury’s penalty decision.
The majority nevertheless seeks to justify the trial court’s ruling by asserting that a capital defendant’s penalty opinion may play an indirect role as an intermediate fact tending to prove some other fact that would be mitigating or aggravating. The majority offers three such facts: “the extent of defendant’s remorse for his crimes, his realization of the seriousness thereof, and his willingness to atone for them by paying society’s highest price.” (Maj. opn., ante, p. 715.) But the majority does not explain how these facts relate to the statutory penalty factors.
None of the three facts cited by the majority relates to the circumstances of the crime, to other criminal acts by defendant, or to prior convictions of the defendant. Thus, they are not admissible under factors (a), (b), or (c) of Penal Code section 190.3.
The facts cited by the majority do have some bearing on defendant’s character, and therefore evidence concerning them could be introduced under factor (k) of Penal Code section 190.3. But factor (k) evidence can only be mitigating; the prosecution’s case in aggravation may not include unfavorable character evidence. (People v. Boyd, supra, 38 Cal.3d 762, 774-775.) *736Nevertheless, if the defendant “opens the door” by offering mitigating evidence of a particular aspect of his character, the prosecutor may introduce rebuttal evidence so long as it relates to the same specific incident or character trait. (People v. Ramirez (1990) 50 Cal.3d 1158, 1192-1193 [270 Cal.Rptr. 286, 791 P.2d 965].) Because I can conceive of no other theory of admissibility, and the majority opinion suggests no other, I assume that this is the basis on which the majority upholds the trial court’s ruling.
Defendant’s testimony on direct examination tended to prove that he had come to appreciate the gravity of the wrong he had done by killing the Shaffers and that he was remorseful. To the extent that it tended to prove these facts, his testimony constituted favorable character evidence under factor (k) of Penal Code section 190.3, and thereby opened the door to rebuttal by the prosecution directed to the same specific traits or aspects of defendant’s character. The prosecutor could, in other words, seek to establish by cross-examination that defendant failed to fully appreciate the enormity of his crimes and did not feel as much remorse as he apparently claimed or as his crimes warranted.
Whether the prosecutor could properly inquire about the third topic— defendant’s “willingness to atone for [his crimes] by paying society’s highest price”—is much less clear. Conceivably, a capital defendant might offer his or her willingness to be executed as favorable character evidence in mitigation, on the theory that it demonstrated remorse and appreciation of the seriousness of the capital crimes, but defendant did not do so in this case. True, defendant told the jury he was not asking them for favors, only fair judgment, but such testimony is a far cry from voluntary agreement to undergo execution. In any event, I perceive no theory under which this topic could be relevant other than to show remorse or appreciation for the gravity of the capital crimes. Thus, the majority has identified at most two aspects or traits of character that defendant placed in issue by his direct testimony.
Of course, the prosecutor did not ask defendant how much remorse he felt, or whether he would willingly be executed. The prosecutor posed a quite different question. The prosecutor asked defendant, in effect, whether execution or life imprisonment without parole would be the more just punishment in this case. I seriously question whether a capital defendant’s opinion as to the just punishment for his or her own crimes has “any tendency in reason” to prove the degree of the defendant’s remorse or the defendant’s willingness to undergo the ultimate penalty of death. (See Evid. Code, § 210 [defining “relevant evidence” as evidence “having any tendency in reason to *737prove or disprove any disputed fact that is of consequence to the determination of the action”].) But I do not pursue this point further, because the majority’s reasoning suffers from a more basic defect.
The majority’s theory of relevance necessarily assumes there is a “right” and a “wrong” answer to the prosecutor’s question. It assumes, in other words, that if defendant had given a different answer, if he had replied that life imprisonment without parole was the just punishment for his crimes, the prosecutor properly could have argued and the jury reasonably could have inferred that defendant’s remorse was insufficient and that he did not fully appreciate the gravity of his crimes. Yet a juror could draw these inferences only by first deciding that defendant’s penalty opinion was manifestly incorrect. To do this—to decide that perpetual imprisonment was inadequate punishment for defendant’s crimes—a juror necessarily would have to prejudge the penalty issue.
Thus, the majority’s reasoning is fatally circular. To be relevant, evidence introduced at the penalty phase must assist the jurors in determining the appropriate penalty. But the evidence at issue here could not be used, and thus was logically worthless, unless and until the jurors determined whether the penalty of death was appropriate.
The majority’s reasoning involves more than a mere logical fallacy. It permits fundamentally unfair cross-examination of a capital defendant in every case in which the defendant, in penalty phase testimony, admits guilt while at the same time expressing remorse and describing rehabilitation. A question calling for the defendant’s opinion as to the just penalty in the case presents the defendant with a Hobson’s choice, because there can be no exculpatory answer. A defendant who replies, as this defendant did, that death would be the just punishment, thereby provides persuasive support for the prosecution’s position and becomes perhaps the most damaging witness against his or her own cause. A defendant giving the opposite response, that life imprisonment without parole is the just punishment, is thereby laid open to the prosecution’s express or implied charge that the claimed remorse and rehabilitation are insufficient or even insincere. Finally, a defendant who declines to directly answer the question can expect the prosecutor to characterize the response as evasive and uncooperative.
For all these reasons, I conclude that defendant’s opinion on the ultimate issue of penalty was irrelevant—that is, it had no tendency in reason to prove or disprove any disputed fact of consequence to the penalty determination. Therefore, the trial court erred in overruling the defense objection to the *738prosecutor’s question asking defendant what he thought his “just punishment” should be.
II
When an error other than a violation of the federal Constitution occurs at the penalty phase of a capital trial, this court must reverse the judgment as to penalty if there is a reasonable possibility that the error affected the verdict. (People v. Brown (1988) 46 Cal.3d 432, 447-448 [250 Cal.Rptr. 604, 758 P.2d 1135].) This is a “more exacting standard of review” than that employed for state law errors at the guilt phase. (Id. at p. 447.) Different standards are warranted by the “fundamental difference between review of a jury’s objective guilt phase verdict, and its normative, discretionary penalty phase determination.” (Ibid) When evidence has been erroneously received at the penalty phase, this court should reverse the death sentence if it is “the sort of evidence that is likely to have a significant impact on the jury’s evaluation of whether defendant should live or die.” (People v. Phillips (1985) 41 Cal.3d 29, 83 [222 Cal.Rptr. 127, 711 P.2d 423] [cited with approval in Brown, supra, at p. 447].)
Here, the improperly received evidence was defendant’s stated opinion that he would vote for death were he one of the twelve jurors. This dramatic testimony could not fail to make a strong and indelible impression on the jurors, and to have a “significant impact on the jury’s evaluation of whether defendant should live or die.” (People v. Phillips, supra, 41 Cal.3d 29, 83.)
How would a reasonable juror make use of this improperly received evidence? If a juror believed the issue of penalty was otherwise close, the juror might overcome any doubts about the appropriateness of the death penalty in this case with the thought that even defendant found this a proper case for a death verdict. This court must reverse the penalty verdict if there is a reasonable possibility that the jury’s sense of responsibility for the penalty verdict was diminished in this fashion. (See Caldwell v. Mississippi (1985) 472 U.S. 320, 328-329 [86 L.Ed.2d 231, 238-240, 105 S.Ct. 2633]; People v. Farmer (1989) 47 Cal.3d 888, 924-931 [254 Cal.Rptr. 508, 765 P.2d 940].)
The majority concludes that the testimony could not have diminished the jurors’ sense of responsibility because the jury was properly instructed regarding its responsibility and because the prosecutor did not mention the testimony during argument. (Maj. opn., ante, pp. 715-716.) I disagree.
*739By overruling the defense objection to the question eliciting this testimony, the trial court necessarily implied that defendant’s “just punishment” opinion was a proper subject for cross-examination, and therefore that defendant’s response had some legitimate role in the process of penalty determination. Nothing in the trial court’s instructions to the jury contradicted this erroneous suggestion. There is no reason for this court to assume that the jurors understood they were to disregard evidence that had been adduced during the penalty trial with the trial court’s express approval. The prosecutor’s silence on the point did not cure the problem; it left the jury with no guidance on the proper use of this testimony.
As repulsive as defendant’s crimes were, this is not a case in which the capital murders were many and of astonishing cruelty, nor is this a case in which the defense introduced little or no evidence of potentially mitigating circumstances. This is not a case, in other words, in which I can say with confidence that the death penalty was foreordained or even highly likely. I cannot escape the conclusion that there is a reasonable possibility that the improperly received evidence affected the penalty verdict. Therefore, I would reverse the judgment as to penalty.
Appellant’s petition for a rehearing was denied December 30, 1992, and the opinion was modified to read as printed above.