Holy Headpat (given to you from dialogue from Lillian about how people "fight" around here) does 1 Holy Damage, though it's obviously a joke move that gets you special interactions from various Mamono in battle.
Demon Layer (also given to you by Lillian after you exhaust her dialogue, have Holy Headpat, and have collected enough sigils plus have 6 or over in Power, Technique, and Allure) is the main source of holy damage in this game, scaling with your virility and Power stat.