Dekisokonai no Monster Trainer  

Dekisokonai no Majuu Renmashi, できそこないの魔獣錬磨師〈モンスタートレーナー〉, The Good-for-nothing Monster Trainer

In this world, every person is born with a unique monster crest. However, only a select few individuals become Monster Trainers. Reyn Erhardt, who trains slimes, disregards social status and focuses solely on his daily training routine alongside his personal slime, Pem-Pem. Despite being in a school where powerful dragons dominate, those who cannot compete rise to the top often take their frustrations out on weaker individuals. Reyn and Pem-Pem become easy targets due to their low status as slime trainers.