so Kira has abandonment issues and thinks herself inferior to Sera somehow? And she seems to think that being in a sister unit is the only way to be next to Sera. Meanwhile, Sera is obviously suffering from inferiority complex towards her little sister, grappling with depression (I'm assuming this) because of how she's working part-time at a maid cafe at her age and her chance of being an idol is close to gone by now.
The ideal way to fix this is for them to talk shit out, accept that being a sister unit isn't needed for they to stay together, and for Sera to take Kyapi's offer if she still want to be popular/being in the idol industry.
But somehow I doubt that will happen.
anw, thanks for the chapter!!