The Devil Is a Part-Timer!, Vol. 7 (manga)

Maou (the Devil King) has a suspicion about the mysterious child Alas Ramus, a wee lass who he and Emi (the Hero) have wound up parenting. During a supremely awkward "family outing" to the amusement park, Emi gets Maou to tell her the truth about their little girl. But when a chorus of angels shows up to settle an old score, Maou's revelation may not matter!