Renkinjutsushi desu. Jichou wa Gomibako ni Sutetekimashita.

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!)