How is that unrealistic?
Some women are that sensitive that they will indeed cum even while a penis is being inserted, I for one am one. ╮(￣▽￣)╭
You know that a lot of authors just make sex scenes short, right?
Good for you, 1%er
Bruh, you know that this is a manga aka picture format. You don't know how much the dude was thrusting into her to make her cum, it could 1 minute ore an hour. And you'll never know because you can't really expect an author to draw every god damn second of a sex scene, they usually draw just the highlights aka inserting, some thrusting and the cum part. So yeah, this is an one shot and you should stop being so demanding.
Cheers you my friend.(๑•ㅂ•)و✧
sticking it in will make her cum in 5 seconds.
And here I thought yaoi stories were the most unrealistic