Responses
Nevermind, I found it!
https://www.mangago.me/read-manga/oita_ga_sugiru_wa_koneko_chan/
I'm not sure how to delete a question sorry.
beta
So I think the MC and ML are related with an age gap. Either uncle and nephew, or cousins and one's older.
The older one is a calligrapher, and when the younger one is visiting he somehow accidentally breaks his arm, and has to stay in his house a while to help him while he recovers? They both have dark hair. Does this ring any bells?