What apartment?
Biggest feature.
1/ Story advancement for Mom (Personal Secretary route)
2/ Story advancement for Aunt (BG Story retconned, she can work with you as Accountant, but only once a week)
3/ Story retconned for Kaya (No longer your secret half sister, her intro no longer ties to Alexia)
4/ Intro delayed for Sex Shop/Salon/Gym girls (Sex shop after Aunt moved out, the other after T1 unlock) So you dont get bombarded with everything at early game.
5/ Story shuffling for Nora (She now gets introduced since tutorial, her serum trait quest changed)
6/ Dates no longer tied to specific day. And there's unlockable date minigames for bar dates. Some dates also ends with 1 night stand.
7/ Starbuck also adding story path system on current develop branch. This allows easier questline to be added to any girls by modders. It's a huge system, and it will take time to convert the currently complete quests to story path, so now develop have 2 quest system running. Starbuck currently converting Camila's quest, so her quest is broken right now. Nora is currently the only girl with full story path system implemented. NOT full quest.
8/ Theres personal events implemented, where basic event (like pregnancy announcement) runs with personalized dialogues, but theres only a few of them. We need more writers!
9/ The biggest change most happens behind the scene, it looks the same, but Trist changing the spaghetti code underneath.
Theres more I think, like the personal serum, but I forgot when it got added. Theres also tidbit of stories spread among minor girls. Oh, city wide topless policy. Never really cared about that, so dunno how to trigger it.