Thanks for your help! It indeed has something to do with attack on titan, this is a -flügel der freiheit- necklace. Thats the symbol of the survey corps but you probably knew that. But those characters are used in Japanese too, right? Kanji or something. I'm probably wrong but I thought these were kanji. Anyway, thanks a lot!The picture is rotated 90 degrees to the left.
Is it something to do with a manga/anime 進撃の巨人 Shingeki no Kyojin Attack on Titan ? Anyway, the characters used there are simplified Chinese, not Japanese, so I suspect it's not an authorized item.