Amakusa Shirou uses

Honestly, not much use. Kit is fairly straight forward. Stun w/ Buster up, star gen per turn, NP gen per turn with a demon/undead tick removal as cherry on top. A rather offensive Ruler. But at the same time, Rulers deal normal to all except BB so............ how offensive can he possibly be, really.

All his skills point towards longevity, but at the same time he doesn't have immunities or innate heal. So if you want him to stay around, might want to run some healing options or immunity for him.

He's very useful during challenging content, like Nerofest, because of his NP which clears buffs before dealing damage. He's one of those specialized Servants that you don't need often, but are invaluable for certain quests.