Gratha

Overview
Gratha is a unique Shadow Ghost, though her genes include a Spectre component. She can be found in a tile event inside a rare shadow biome inside portals if the entire team is of the Dark type, including the Main Character.

If the player chose the shadow elemental affinity at the start of the game, there is an option to craft a special recipe that permanently changes a character's type to Dark. Evolution can fulfill this criterion by shapeshifting into a Dark unit and a natively Dark 4th MC fulfills it naturally, but options for other MCs commit permanent changes to the character.