Depicting the story of a shut-in, Kirihara Yukito, after being reincarnated into another world.
His peaceful life with his precious caring sister, Sana, suddenly come to an end when a beast appeared and attack them, thus reincarnating him into the “Ever World”. Moreover, knowing that Sana also got reincarnated into the Ever World, for the sake of finding his beloved little sister he begins his journey in another world….

(Source: Endless Journey)

One of the most powerful demon lords ever has been sealed away for a thousand years. When he finally awakens, he is reincarnated as…a 10-year-old boy?! Now under the care of the girl who released him, the demon lord Leonis must navigate the perils of Excalibur Academy!

(Source: Yen Press)

From MangaHelpers:

This is a manga based on a popular light novel series of the same name.

Kazehaya Kamito has been summoned to the girl's school Alessia Spiritual Academy, which teaches noble young ladies how to make contracts with powerful spirits. On his way, he has the misfortune of catching sight of one of these lady spirit contractors bathing. She is Claire Rouge, and she is contracted to a spirit named Scarlet, though she has her sights set on a more powerful spirit. Kamito convinces her to lead him to the school, but she stops on the way to make a contract with this powerful spirit. When Kamito ends up 'stealing' the powerful spirit, it is revealed that he is actually an unheard-of male spirit contractor! What could be the origin of his power? Now Claire is determined that he's going to have to support her, since she believes that the spirit he now has power over what should rightly be hers... [tethysdust]

When the Chemistry teacher secretly practices witchcraft at normal school, many things can go wrong! Fuyumi Renji realises this as Kirise Ririka somehow walks through all his magic barriers and interrupts his spellcasting! How could a normal high school girl ever be able to do this?