Oooooooooooookay! Rin Tsubokura was originally a character created by Kubo as a mascot for the Japanese Bleach-Fan news site. It seems that he became so popular that Kubo decided to put him in the manga and the anime. He is a timid scientist of the 12th Division that likes sweets and jumps at the chance to go to the real world just to buy sweets unavailable in the Soul Society. He first appears in chapter 190 of the manga.