Dekisokonai no Monster Trainer

Dekisokonai no Monster Trainer (できそこないの魔獣錬磨師〈モンスタートレーナー〉, Dekisokonai no Majuu Renmashi) is a light novel series by Takumi Minami with illustrations by Koin. A manga adaption with art by YUI is serialized in Comic Alive.

Plot
In a world where everyone has a monster crest since birth, only a select few rise up to become Monster Trainers. Reyn Erhardt, a slime trainer, the lowest of the low, cares nothing for status and just continues his daily training regimen together with his personal slime, Pem-Pem.

In a school dominated by monsters as powerful as dragons, those who cannot hope to rise to the top take their frustrations out on the weak, and Reyn and Pem-Pem make for easy targets...?