Thank You, Yuri
Most mods install on top of a fresh copy of DDLC, free from ddlc.moe. Follow the author's instructions, and keep a clean copy of the game.
About this mod
It's nothing special; it's just a mod showing how powerful Yuri's friendship with Sayori is. Kinda similar to the friendship between McQueen and Teio, if you think about it. To install this mod, it actually works in the reverse order than you're used to; just put all .rpa files except for scripts in the /game folder of the mod (don't dump the mod files into a base game copy) and click on whichever executable works for your OS (so, for Windows it's TYY.exe)