18+ Love 2 Quad

One day, the most popular teacher at Akakura Gakuen, Aoi-sensei, approached Wataru and informed him that his help is needed and he must take off his clothes immediately. She was an agent of the secret international defence organization Cradle and asked him to aid in the battle against the enemy "4D". In order to defeat "4D", he must engage in ecchi activities to gain energy and defeat the enemy with the power of love! His imouto-like osananajimi Honoka, classmate Ermalit, expressionless Mirai from the future and chibi Chitose from the past lend their help. However, they aren’t sure what to do!? And so marked the end of his peaceful single life.

(Source: VNDB)