Chiyu Mahou no Machigatta Tsukaikata: Senjou wo Kakeru Kaifuku Youin

Usato, an ordinary high schooler, happens to run into two fellow students after school one rainy day. Suddenly, all three of them are engulfed in a magic circle and transported to a fantasy world. There's just one tiny problem—Usato is simply dragged along by accident! On top of that, Usato learns that he is capable of using healing magic—an incredibly rare affinity in this new world. Now Usato must spend his days with the rescue team thugs, struggling through their hellish training regimen—learning the wrong way to use healing magic. Get ready for an eccentric otherworld fantasy filled with comedy and combat!

(Source: One Peace Books)