Well, I guess it's hentai so it doesn't have to make sense but uh. How the hell would they even catch her in the first place?
Servants can shatter steel like clay. They can turn intangible. outrun cars, ect.
And that's ignoring that a seal like that probably wouldn't work anyway.
Some people might like this. Yet this is incomplete. Also it's weird as the kid is trying to claim is friends mom? Also the guy doesn't stop him either so he let him do it anyways. Worst part if the ending was with her pregnant that guy would have no clue how annoying that responsibility can be. This would be better if it was thought about more and fleshed out better.
Servants can shatter steel like clay. They can turn intangible. outrun cars, ect.
And that's ignoring that a seal like that probably wouldn't work anyway.