Declare me Co-Emperor

is_available = government_has_mechanic = administrative
trigger_if = {
	limit = {
		is_ai = yes
	}
	NOR = {
		has_trait = content
		has_trait = humble
	}
}
top_liege != this
is_shown = scope:recipient = {
	this = scope:actor.top_liege
	may_appoint_co_emperors_trigger = yes
}

As written in game/common/character_interactions/06_ep3_interactions.txt.

scope:actor = {
	valid_co_emperor_candidate_trigger = {
		LIEGE = scope:recipient
	}
	NOT = {
		is_at_war_with = scope:recipient
	}
}
scope:recipient = {
	is_at_war = no
	has_active_diarchy = no
	trigger_if = {
		limit = {
			exists = designated_diarch
		}
		time_after_diarch_designated = {
			years >= 10
		}
	}
}

As written in game/common/character_interactions/06_ep3_interactions.txt.

on_accept = scope:actor = {
	send_interface_toast = {
		type = event_toast_effect_good
		title = declare_me_co_emperor_interaction.tt.success
		left_icon = scope:recipient
		scope:recipient = {
			custom_tooltip = {
				text = declare_me_co_emperor_interaction.tt.effect
				try_start_diarchy = co_emperorship
				set_diarch = scope:actor
			}
			if = {
				limit = {
					scope:actor = {
						is_child_of = scope:recipient
					}
				}
				designated_heir ?= {
					if = {
						limit = {
							this != scope:actor
						}
						custom_tooltip = appoint_co_emperor_interaction.tt.overwrite_designated_heir
						save_scope_as = old_heir
					}
				}
				hidden_effect = {
					set_designated_heir = scope:actor
				}
			}
		}
	}
	if = {
		limit = {
			scope:hook = yes
			has_usable_hook = scope:recipient
		}
		use_hook = scope:recipient
		reverse_add_opinion = {
			target = scope:recipient
			modifier = suspicion_opinion
			opinion = -20
		}
	}
	if = {
		limit = {
			scope:gold = yes
		}
		show_as_tooltip = {
			pay_short_term_gold = {
				target = scope:recipient
				gold = scope:recipient.request_co_emperor_interaction_gold_cost_value
			}
		}
		hidden_effect = {
			scope:recipient = {
				add_gold = request_co_emperor_interaction_gold_cost_value
			}
		}
	}
	tgp_activate_catalyst_against_hegemon_effect = {
		HEGEMON = scope:recipient
		CATALYST = catalyst_hegemon_influenced_by_interaction
	}
}
if = {
	limit = {
		scope:influence = yes
	}
	scope:recipient = {
		change_influence = scope:actor.request_co_emperor_interaction_influence_cost_value
	}
}
scope:actor = {
	set_variable = {
		name = co_emp_appointer
		value = scope:recipient
	}
}
if = {
	limit = {
		exists = scope:old_heir
	}
	diarch_overwrites_old_designated_heir_apply_opinions_effect = {
		LIEGE = scope:recipient
		CO_RULER = scope:actor
	}
}
on_decline = scope:actor = {
	send_interface_toast = {
		type = event_toast_effect_bad
		title = declare_me_co_emperor_interaction.tt.failure
		left_icon = scope:recipient
		if = {
			limit = {
				is_ai = yes
			}
			add_opinion = {
				target = scope:recipient
				modifier = insult_opinion
				opinion = -40
			}
		}
		change_strife_opinion = medium_strife_gain
	}
}

As written in game/common/character_interactions/06_ep3_interactions.txt.