i love your tat, and i also have kanji lettering on me. mine is on the back of my neck and means star, for what my mom wanted to name me so when i upload it wwe will se what ol' bob has to say about it!
Sorry to tell you this, but these 2 characters do not say "sister." In order to read "younger sister," they would have to be combined as one single character. What you have reads something like "not yet woman." The characters are pretty bad too.