Keiki's manga / #Adventure(2)

They are the great mage family who died out after the great demon war. Only MC and sister remain. Their vassals betrayed them. He wants to bring the fmily name up but he has blockage disease, he can't use magic, although he is a genius in magic theory. He went to dragon's nest where he absorbed 1st demon king, mephisto. He also acquired dragon heart and can now use dragon magic. Family heirloom that absorbs demons. Ancestors' tests.

Likeable male lead. Humble. Op. Accidentally killed by wind god, reincarnated in another world. Entrusted to care for the water god's children. Given familiars by water, wind, fire and lastly earth gods. Infinite storage. Items. Cooking. Labyrinth. Friend with nobles, royals.