Rebirth

After both L and Light die, they are reincarnated into a new world. A parallel dimension where swords, guns, and spells are used in battle against mythical beasts. At first, L is hesitant about killing, but after realizing that his survival depends on it, he accepts using his guns. Light is completely against killing having noticing how childish his past beliefs of justice were, but hidden within him is Kira, and an instict to kill. When a mysterious genocide occurs in their area, L joins a group of local investigators to find out who was behind the killings and sees that Light had joined as well.

(I assure you, it is L x Light)