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
The protagonist and Sayori arrive at the club as usual. However, today is special because it's the club's 2nd anniversary! They go over to the clubroom to find it all decorated. Then, the tide turns when some unexpected visitors show up...