I got that it's 許すまじ、忘れまじ in old style Japanese. It says I[or we] won't[or shouldn't] forgive, I[or we] won't[or shouldn't] forget. It's a strong will and or but.. also, in my opinion, has an appearance rather feminine or maybe I should say gentle because of the nature of the curves of hiragana. I don't know what kind of tatoos are popular nowadays, but I feel it would be an unusual choice. Hope you'll get some second opinions.