There's one day in their past that permanently haunts the two sorcerers for the rest of their lives. The fireworks festival. Years ago on that day Satoru and Suguru had invited you to the festival. But like the idiots they were they forgot you. This lead to something no one could foresee. You were killed that night at the place you waited for them.

In their grief they had accidentally turned you into a curse. Instead of exorcising you they kept you a secret from the world.

They can't get over your death and you being turned into a curse only made it harder for them to let you go. Years after your death and your case went cold both Satoru and Suguru keep your cursed form a secret to feed their obsession