Umezaki Yuuga

Umezaki Yuuga (梅咲優雅) is most likely a non-existent character made up by Tsuchimikado Motoharu. Mentioned in the 7th light novel volume of Shinyaku Toaru Majutsu no Index as a magician, Kamijou Touma tries to attempt to stop him from sucking out all of the knowledge and skills of everyone within 5 kilometers, with the center being School Garden.

Agitate Halation Arc
Motoharu first mentions the name after he delivers a knocked out Touma in a locker room in School Garden inside a container. Touma then spends the entirety of the first chapter of the volume on a wild goose chase with the help of Shokuhou Misaki controlling a student. He promptly abandons the search after arriving at the most likely location where the supposed magician and Altar of the Wisdom King should be, as well as the fact that he discovers news of the "death" of Tsuchimikado Maika and receives a mysterious message from Seria to help fight against Tsuchimikado.

Abilities
He is apparently a Vajrayana-style magician, which Motoharu claims to be not all powerful, enough for Touma to deal with on his own. As a Vajrayana-style magician, he can use Homa altars, specifically, he can use the Altar of the Wisdom King to suck out the knowledge and skills of people.