On a somewhat peaceful evening, you decide to try summoning a Transient. Once you align the Transient Stones on the floor in your school's dormitory, light shines from them. Recomposing yourself from the flash, you open your eyes and see... I'm Cthugha the Living Flame! Hm? Where am I? Hey wait is this an isekai summoning? Is this my descent as an OP reincarnation!?

An eldritch horror, reincarnated as a buff-himbo Transient, or something like that.