Barnaby couldn't remember if he said so at the time, but he must have at least thought it, that the first birthday he spent with Kotetsu as part of a couple was probably the best birthday he had ever celebrated. Objectively speaking, Barnaby knew he had no reason to come to that conclusion—Barnaby had never really cared about celebrating his birthday, so it couldn't be that that was what made it so special. They didn't do anything special (dinner and a movie) but for some reason, it felt like the best birthday ever.
