^It wouldn't make much sense for him to transfer his life force into him considering he was already dead at the time. We've seen Hagoromo or other Otsutsuki give out their chakra, or power, onto living beings already. However, we haven't seen dead beings pass their 'spirit' or person into another physical entity.
For example, Minato and Kushina transferred pieces of their chakra (life force) into Naruto's seal so that they could live in him for a required moment that he would need their help. It didn't last forever. Even Sasuke ended up absorbing Orochimaru inside of him, but it was a forceful act rather than Orochimaru doing it himself.
On that note, it doesn't really make sense for Momoshiki to transfer his power because his ability lies with:
> Absorbing Ninjutsu
> Sending that Ninjutsu back stronger
Its hard to say what the seal does, its too early to tell. Though I'll warn people not to immediately judge its properties because Kawaki also has the same seal, and I doubt that Momoshiki 2.0 is living inside of him as well. Most likely the alien that gave it to him is alive and breathing, unless he somehow killed one singe-handily :lol
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When we found out that the seal originated from the hand, I looked back in the chapter and the author did hint that the seal was originating from the palm instead of the outer-hand.
It looks like it grows, unlike the normal Curse Seals who grow when turned "on" -- The seal actually grows in its 'normal/base' mode until it gets turned 'on' (and glows)
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It is also possible that this might be Kawaki's 'seal'
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