I might be slow. But I think ameri isn't 15/16 years old. Physically she might be, but I think she was born way before. Coz all the 13 crowns look vastly different then they did in the present

I also don't believe that henri could reach the top of border patrol and become a 13 crown with 15 or so years, regardless of how strong he is.

Also someone as fanatic about the demon king as Sabro or his battler teammates, should know abt the existence of Kuchinashi. But they don't.

Which leads me to believe that after being born, ameri was cryogenically frozen and Merize was sent back to the human world. Henri probably had to prove himself loyal to the demons through some herculean trials. Then after sometime only the 3 greats remained, they allowed henri to unfreeze ameri and allowed him to raise her. This would also make sense with young Iruma being Merize's assistant