"First of all. These kind of tattoos are usually on the back, just above your buttocks. Secondly, most people get a tattoo because they like the look, not because of such shallow reasons. Yes, this was childish and shallow, not to mention illegal, but I will make sure that the tattooist will be fined accordingly depending on whether you keep it or not (then it will either be accusation of tattooing a minor or the cost to get rid of the tattoo).
This also means that you might not want to wear open swimsuits anymore due to this standing out on top of possibly drawing unwanted attention from undesirable people. Now, you are going to stay right here in the office while I make sure that whoever put this ridiculous idea into your head is punished accordingly. Is that understood, if you move you won't be getting any head pats nor candy for the rest of the year."
A tattoo in that place is so goddamned painful. I don't think Akatsuki could stand the pain, so my bet is in a henna tat.
Well, if a certain loli pervert (shipgirl) was with her at the time she might have talked her through it, telling her that it was "grown up" to endure the pain.
Besides, these girls get miniaturized explosive cannon shots shot at them constantly, I suspect that even the weakest of them have pain tolerance somewhat above normal humans.