Ookami wo Katteimasu

Ino, an expressionless and unsociable office worker, lives with a younger man who is in love with him like a dog with its master. Even though the two of them barely know each other, Taichiro suddenly volunteers himself when Ino and his colleagues put out a drunken call for candidates to be Ino's partner. Ino turns Taichiro down, but because Taichiro has no home to go back to, Ino offers to let him live with him. Taichiro is patient, and although he sometimes can be touchy and steadfast about his love for Ino, he makes sure never to do anything that Ino won't like. One day, after starting to come to terms with his own feelings for Taichiro and his boundless devotion, Ino falls into a suspiciously deep puddle and somehow enters a parallel world. He finds Taichiro there, but in this world, the two of them are complete strangers, and Taichiro's cold demeanor seems to be almost the complete opposite of the man Ino knows and loves... (Source: Renta!) Note: Includes 1 extra chapter.