Senmetsu Madou no Saikyou Kenja - Musai no Kenja, Madou o Kiwame Saikyou e Itaru

From Manga Up: Despite being born with the crest that's most unsuited for battle, Gaius devoted his life to researching magic and became the world's strongest mage. Still, he yearns for more formidable enemies, even though he's painfully aware of how powerless he would be against them. And so, he goes in search of allies. But who would be fitting for the strongest battle mage? Meet Iris, the Dragon of Darkness in a young girl's body; Yuril, the Sorceress of Annihilation, known as the strongest in the kingdom; Reuter, the Demigod of the Blade, and his skills are worthy of being praised in legends. Join these four as they go through battles that transcend imagination.