Great little VN! I love it.
I was fiddling around with some renpy tools, trying to figure them out, and ended up making a couple little script mods for this.
The Holly one makes Holly into the player character's little sister, instead of Louise's little sister. And the full one makes Holly into the player character's little sister, and makes Louise into the player character's big sister. They both edit lines and add some new ones.
I spent like an hour trying to figure out how to compile it into a .rpa file that you can just drop into the game folder like other patches I've seen on this site, but I couldn't figure that out. So the zips are just the edited 1_ch1.rpy and 2_ch2.rpy files (from /game/scripts folder after using un.rpy to decompile them). But I thought I would share them anyway.
(First post haha, hope I didn't miss a rule about this sort of thing.)