Just an idea but maybe add a route where mc's sister decides to eat her
like maybe mc's sister gets her drunk and slowly gets her to strip naked pushes her unto bed and proceeds to put mc's feet in her mouth and decides she is to delicious to let out and decides to digest her
and mc has 2 choices 1 she gives up and mc's sister has second thoughts and decides to release mc or 2 you struggle and mc's sister decides she will release mc for now and will break her sisters will and make her accept that she is food after 3 more events where she forces mc's cloths off and swallows her on third event mc accepts shes food and strips lays down and feeds her sister