She is happy Riku wants her, but she can't be with him. Some secret phone calls suggesting she will "disappear soon". Takt being shady as fuck and probably gay, them being a couple with Shizuku seems a fake deal to hide Takt gayness.
My theory is that she has some family issues that Takt will help her solve, like huge debt or expensive possibly oversea medical operation that cost a lot, and she became his fake GF to hide his gayness and keep her away from Riku, cause it seems Takt hate seeing MC with females so he steals all of them if he can, while trying to "fix his gayness" - hence that talk about Umi and him "looking for a replacement". Shizuku can't date MC cause probably the money borrowing deal stops her from doing so, but it doesn't stop her from jumping his dick, cause we already know she wants her first time to be with him.
This whole operation/stuff, wanting to lose virginity with the boy she loves but can't date/be with, so she is happy to let the "rapist" fuck her after she does the deal with MC, could actually work as a reason for the rape dude to "lose interest" if author is an idiot and thinks rapists work that way.
Thou people spoil author spoiled the ending will be traumatic. So like operation fails and she dies? MC find out, maybe even about the deal and the whole Takt being gay? And it somehow ruins the trio friendship, cause Shizuku is dead, and MC stops being friends with Takt cause of the deal/gayness?
This idea kinda scares me, cause MC ending up in a relationship with the "new" girl, and her ending up being the only normal non "raped/NTRed" among the females, kinda contradicts the traumatic ending. MC loves Shizu hence why he wants her to be his, her dying would trauma him, and he would for sure reject Umi and best girl.
