Because he was born on December 24th, and his parents named him Santa.
Rough break.
She collapses with laughter.
But no, she says, okay, it was kind of funny, but she wants to make him happy.
He says to leave him alone, he's perfectly happy the way he is.
This is a lie.
This is mediocre in every way. The animation isn't great. The writing is super basic.
Like most Christmas movies, it's churning out cheap work to make a buck on a guaranteed sale.
But Japan isn't a heavily Christian country, so I'm not sure how guaranteed the sale is.