korea_unify_goryeo_reward_effect

korea_unify_goryeo_reward_effect = {
	# Legend Seed
	gain_heroic_legend_seed_tooltip_effect = yes
	# Create new titles
	create_title_and_vassal_change = {
		type = created
		save_scope_as = title_change
	}
	title:e_goryeo = {
		change_title_holder = {
			holder = scope:king_of_goryeo
			change = scope:title_change
		}
	}
	resolve_title_and_vassal_change = scope:title_change
	# Destroy old titles
	title:k_silla = { add_to_list = korea_kingdoms }
	title:k_baekje = { add_to_list = korea_kingdoms }
	title:k_goguryeo = { add_to_list = korea_kingdoms }
	every_in_list = {
		list = korea_kingdoms
		limit = { holder = scope:king_of_goryeo }
		save_scope_as = korean_kingdom 
		scope:king_of_goryeo = { destroy_title = scope:korean_kingdom }
	}
	#If owned, annex Balhae.
	if = {
		limit = { title:k_balhae.holder ?= scope:king_of_goryeo }
		title:k_balhae = { set_de_jure_liege_title = title:e_goryeo }
	}
	# Rename Ceremonial throne if relevant
	title:k_yongson_throne ?= {
		hidden_effect = {
			if = {
				limit = { scope:king_of_goryeo.culture = culture:silla }
				set_title_name = "cn_silla_throne"
			}
		}
	}
	# Cultural acceptance (move towards Goryeo culture)
	every_culture_global = {
		limit = {
			NOT = { this = scope:king_of_goryeo.culture }
			OR = {
				has_cultural_pillar = heritage_buyeo
				has_cultural_pillar = heritage_korean
				any_parent_culture = {
					OR = {
						has_cultural_pillar = heritage_buyeo
						has_cultural_pillar = heritage_korean
					}
				}
			}
			any_culture_county = {
				any_county_province = { geographical_region = world_asia_korea }
			}
		}
		add_to_list = goryeo_cultures
	}
	every_in_list = {
		list = goryeo_cultures
		change_cultural_acceptance = {
			target = root.culture
			value = 25
			desc = cultural_acceptance_gain_unify_goryeo
		}
	}
	set_global_variable = {
		name = flag_united_the_husamguk
	}
}

As written in game/common/scripted_effects/10_dlc_tgp_korea_scripted_effects.txt.