Mila knows more than G gave her credit for

"Why is this wound infected, Gaster?"

"What?"

"I was expecting to just heal the burn Asgore accidentally gave you. What is this thing on your ulna?"

"I just... cracked it a little, Mila. During training a couple days ago. That's all. N-nothing - big - ow!"

"It's okay. I'm not mad at you. I just wanted to know why you didn't think to get something this bad healed."

"It's no big deal, it's not my dominant arm and my magic is usable."

"No big deal? I'm equally scared and impressed that you hid something this painful for this long. But please... don't. Let me help."

"But I have to keep going. I can't afford to miss... aaaagh!"

"Sorry! Just... who told you to ignore this kind of thing? Any healer can tell you that it's important to start treating an injury as soon as possible, and then rest properly afterwards, so that the recovery has the lowest chance for complications."

"What do you mean who told me? That's just how things are. I can't be weak."

"...it's your father, isn't it. Roman. The old general."

"What about my father?"

"He told you the world was like this. He told you that the world would be even crueler than he would be, and that's why it was okay to hurt you. Right?"

"...well..."

"And that's why you have a poorly healed spiral fracture on your humerus here and multiple crooked toes."

"Wh... that was..."

"I didn't want to pry, in case it was something you were trying not to think about on purpose. But... would you think it was okay if some other child's parent had forcibly twisted their arm until it broke like that?"

"I'm stronger and more talented than anyone else my age. I should have been able to prevent it from happening."

"There’s teaching a child to be strong, and then there's actively brutalizing them. Training works best when it's exploring and stretching your capabilities. Not when it's throwing you against a wall and hoping it breaks before you do."

"..."

"Okay. Most of this should be healed, or else stabilized well enough to heal on its own. I'll come back tomorrow. I will, however, tell you now that the typical recovery time for a healing of this extent is three days. If you try to get back to training before two and a half I will tell Rin to put you back in bed. Forcibly if necessary."

"...thank you. I'm sorry for being trouble."

"I'm glad to do it for any of my friends. And please. Give yourself more credit. You matter too."