Nazeka Tsukaima no Usagi wa Boku wo Dekiai shisugiteru

Aidan McGuire is a new magician in the Guardians of the Order. Every Guardian has a humanoid familiar, and summoning one is mandatory! But during the summoning ceremony, Aidan summons a cute rabbit! He was told "deeper contact" was necessary for the familiar to showcase its true power... so when he tried kissing it, the rabbit disappeared and a young man named "Hidetora Jougasaki" appeared in its place! A cute (!?) fantasy BL story about a magician with a vague memory of a past life.

(Source: Kadokawa, translated)