Leo

He calls himself a "Great Scholar" and carries a certificate of the association, but his name is not seems to be listed among them.
He's a man of mystery.
He spends his days quietly enjoying cups of tea and reading books in a western style mansion in a corner of the of "Water City", with his assistant Liza Fourth.

His true identity is Leonardo da Vinci, the sixth of the Ten Great Scholars, the "Omnipotent King".

He's the protagonist of the first part of the final chapter.