Number of works of fiction that made me shed at least one tear: 3Thou seeketh soul power, dost thou not?TOX: 33524385841A92B08787EEBEBA2DB51ED293C4F15A2E292F3F C92165E82388281433A77EA8FE
And what about in Death Billiard, where the dude smiled as he was sent to the void? The mask there didn't change at all either. I don't think this theory stands because participants aren't necessarily told where they're going, so subjective feelings about their destination affecting the mask would be strange.
If it's not Isuzu-chan Mii~