Futsuu no Oni-chan

Getting demoted from a Royal Magician into a Potion Factory, Yulius led a hopeless life. Until one day elf sisters suddenly kidnap him into a desert country, Shambala... Hearing pleas for rescue from the Beauties, he creates an experimental squishy potion, an elixir! Dungeon exploration, waterway construction, landscape restoration etc... Splendidly switching from a genius Magician into the strongest Alchemist and saving Shambala, what future awaits Yulius!?

From Google Translate: The reincarnated Alexant awakens to the memories of his previous life at the age of seven. Then, when he turns 13, he enters the prestigious Akasha House school. There, he displays many talents, but then he encounters alchemy. "Live an interesting and fun life with alchemy!" Alexant enjoys his life to the fullest, enjoying the hectic school life with little witches, loli elves, energetic dark-skinned girls, and more!