Ikui Sora

Due to a god's mistake, high schooler Tsuguna died before his time. In exchange, the god agreed to do him a favor in his next life. Tsuguna is reborn to a noble household in a world with magic. He has an unusual form of magic that he requested from the god, the ability to create summoned creatures. However, his dark Japanese hair and eyes mark him as a cursed child in this new world, and his powers are slow to appear. He's kept in a dark basement where he reads his family's books, until one day he finally uncovers the key to his powers. Finally, he can set off into the world with his summoned companion to level up his skills!

From MangaHelpers: Due to a god's mistake, high-schooler Tsuguna died before his time. In exchange, the god agreed to do him a favor in his next life. Tsuguna is reborn to a noble household in a world with magic. He has an unusual form of magic that he requested from the god, the ability to create summoned creatures. However, his dark Japanese hair and eyes mark him as a cursed child in this new world, and his powers are slow to appear. He's kept in a dark basement where he reads his family's books, until one day he finally uncovers the key to his powers. Finally, he can set off into the world with his summoned companion to level up his skills! \[tethysdust] (Based on a light novel.)