Okay this story is good but wtf is wrong with that black haired gal okay i know she has he...

Well whoever the father is (only see blurry figure) ordered or threatened her to kill it. I'm assuming it's because of him that the baby can't go to police station, perhaps getting baby killed for sure and more abuse for her if someone turned it in.
Still shitty, but a small chance it better than no chance.

Under the bridge is still too neglectful. She could have travelled to a police or fire station in another city or prefecture and abandoned him where people are actually around and see him. i doubt the father would go out of the way and kill it that far from home. It'd be making it a bigger scheme than necessary and reveal his involvement.

isn't it likely that they'd run some sort of test to find out his parentage and then contact his parents? which would lead the baby back to the abusive ass (because he's be obligated to come and pick him up) and the neglectful girl. the baby would be killed and the highschool girl would suffer more abuse and stricter restrictions because she lied to him once, she can do it again. It was probably the best a highschool girl could have done at the time. leaving it under the bridge meant that she could have a slightly cleaner conscience but also decrease the chances of the baby being found by adults and taken to the police.

No, not in my country at least. The law says that if you abandon a child in front of a public place like a police station or hospital there is no questions asked or legal actions taken and it goes into the foster care. And if she was worried about that, that's why I suggested going to another city or prefecture. It'd be harder to connect them to the child if you're a stranger to the area.

Huh, I didn't know that. Makes sense though I guess. At the same time I also think.It's for plot reasons but this is what you'd probably call plot hole. Well, thanks for explaining it to me! Have a good day.