>>137440I believe the purpose you talk about ties into, at least as I see it, the theme of interrelation.
The people who best manage to survive are those anchored to someone or something, and the fundamental problem is that Sis destroyed the fabric of those relationships in her pursuit of absolute freedom and truth. Tkmz is definitely sending a message by having her sacrifice herself to undo her mistake, and framing said truth (which Yomikawa partly dismisses, partly admits) as secondary compared to the two's relationship taking the final spotlight. It's also interesting how their greatest moment mirrors their lowest, where instead of blurring out they reassert their boundaries in a mutual act of acceptance and intimacy.
I wouldn't put as much emphasis on their gained powers though, to me the former is a straight continuation of how the setting works. It's shockingly consistent in its writing, if you take the time to look into it.