apply_clan_unity_interaction_effect

apply_clan_unity_interaction_effect = {
	# Save scopes for localisation
	$CHARACTER$ = { save_scope_as = unity_character }
	$TARGET$ = { save_scope_as = unity_target }

	$CHARACTER$.house = {
		save_scope_as = character_house

		add_unity_value = {
			value = {
				value = $VALUE$
				if = { # House heads have a larger impact on unity
					limit = { house_head = $CHARACTER$ }
					multiply = unity_house_head_multiplier_value
				}
				if = {
					limit = { $VALUE_REVERSED$ = yes }
					multiply = -1
				}
			}
			character = $CHARACTER$
			desc = $DESC$
		}
	}

	# Notify human players if they are not involved!
	if = {
		limit = {
			trigger_if = {
				limit = { $VALUE$ >= 0 }
				$VALUE$ >= major_unity_value
			}
			trigger_else = {
				$VALUE$ <= major_unity_value
			}
		}
		# Notify human players if they are not involved!
		notify_players_about_unity_change_effect = {
			CHARACTER = $CHARACTER$
			TARGET = $TARGET$
			DESC = $DESC$
		}
	}
}

As written in game/common/scripted_effects/00_interaction_effects.txt.