Boku Kano 2 ~ Osananajimi ni Senpai ni, Mayoeru Otoko no Sankaku Kankei

Jun and Shinji were childhood friends who grew up together.
They attended the same schools and protected each other.
But once separated to go to academy,
Shinji went mad with worry.
Was Jun okay? Was she being teased?
After only a short time Shinji decided to save her.
He dressed up in girl's clothes to infiltrate her school...!

[From dlsite]