At certain chapters there are "flashbacks" of them together in the dorm where they shared a room - the second time they met after Klaus met Taki when he was having his "coming of age" ceremony.
You may feel your favorite manga should be gathered together into distinct categories for your own reference and, now, you can do this with a LIST. After you've created your list or lists, you can proudly recommend them to other manga fans to showcase and share your taste in manga.
Boku ni Hitsuyou na Mono