The Failure of a Monster Trainer is a Manga/Manhwa/Manhua in english language, Action series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.nl fastest updating comic site. The Summary is

In a world where everyone has a monster crest from birth, a select few rise to become Monster Trainers. Reyn Erhardt, a slime trainer, the lowest of the low, cares nothing for status and just continues his daily regimen of training for his personal slime, Pem-Pem. Yet in school dominated monsters as grand as dragons, those who cannot hope to rise to the top takeout their frustrations on the lowest ones, and Reyn and Pem-Pem make for easy marks. Or do they?