Tsuki no Oki ni Mesumama(2018)

Tsuki no Oki ni Mesumama

In middle school, Ayumu kept getting teased and pranked by Runa, even though he's a year younger than her.
Now that she's in her second year of high school, she's ready to be the experienced senpai for the incoming freshman Runa.

Note: Chapter count includes two epilogue bonus chapters.