A real longshot here. There was one chapter/scene where the MC? asks for tea and it wasn't brewed correctly. MC then explains how kettle would lose like 8 degrees celsius when moving from one vessel to another or something. I think MC is a lolita... possibly gothic lolita type and other character is a nerdy type who becomes her servant or something

What you're describing really sounds like the Celeste and Hifumi scene in Danganronpa: Trigger Happy Havoc, though I've never read the manga for that, so I don't know if it's what you're thinking of, since I remember this scene from the actual game itself.