I’m an Alchemist Who Doesn’t Know How OP I Am

Also known as: Renkinjutsushi desu. Jichou wa Gomibako ni Sutetekimashita., 錬金術師です。自重はゴミ箱に捨ててきました。, He's an Alchemist. His Own Weight Has Been Thrown Into the Trash.

by You Toraku, Ryou Kazuki

In order to save her little sister's life, S-ranked adventurer Laffey seeks an all-healing elixir. However, elixirs are highly precious items that take years to make by even the most experienced alchemists. But one day, she meets a man that defies these rules! "Here, an elixir. Oh, it's fine, I can always make more." A slow-paced fantasy about an extraordinary alchemist who doesn't know his own worth and a beautiful adventurer girl who gets caught up in his efforts to help others! (Source: MANGA UP!)