Ore dake Chou Tensai Renkinjutsushi - Yurui Atelier Seikatsu Hajimemashita

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!