Main character Zack has hit rock bottom. His family hates him, and his fiancée called off his engagement. A black object appears before him. It turns out to be Sura, a powerful black slime that speaks human!
My Partner is a Slime!?: With the Strongest Partner, I'll Use the Strongest Magic to Rise in the World is a completed manga by Nanjamonja (なんじゃもんじゃ), first published in 2021. It blends comedy and adventure. You can read all 13 available chapters of My Partner is a Slime!?: With the Strongest Partner, I'll Use the Strongest Magic to Rise in the World online for free on MangaPulse; the newest is Chapter 11, added 2026-07-22. The series is finished, so you can read it from start to end in one go.