The manga you're referring to is likely "Welcome to the NHK" (NHK ni Youkoso!).
Related Q&A：
Well, that sounds like an interesting premise for a manga! There are a few possibilities that could fit this description. One manga that might come to mind is \My Strange School Life.\ In it, the girl with OCD faces new challenges at her transfer school and her encounter with the odd guy leads to unexpected adventures and self-discovery. Another option could be \Confessions of an OCD Girl,\ where the story focuses on her experiences and how the strange guy becomes an important part of her journey. But it's hard to be sure exactly which manga you're looking for without more specific details.
