The Incredible Kintaro

Makoto's grandfather was the principal of the great Onodera Academy, and when he passed away, he left Makoto and his school staff with one very important will - "The one man who is able to seduce Makoto with his superb sexual techniques will be given the right to take over as Onodera Academy's new principal!" Because of this ridiculous last request, Makoto is now every faculty member's target for sexual harassment! Desperate to protect his virginity, Makoto seeks help from his childhood friend (and the man who he has always loved), Kintaro.

(Source: DMP)

Note: Includes one extra chapter.