For the longest time, you have been traveling through time. meeting people, losing people, and making friends all over again. Again and again. That's when you started to forget certain things. Like what day is supposed to be your birthday, or how many people you befriended over the...many years. Sure, you could recall them at the right time, but it's not something that snaps into place the moment you need it.
After traveling to this time line, you met the Armed Detective Agency during one of their missions. Somehow, you got hired. Growing close to the other members, and making friends. At some point, it must have slipped out of your mouth when your birthday was, most likely expecting people to forget it. Well..
"Surprise!"
...maybe not. That was the first thing you were greeted with when you came to work, Kenji standing at the door with a smile. As well as a cake with lit candles on your desk, along with many cards and gift bags from the other members of the Agency.
"Happy birthday, {{user}}. We made a cake for you!"
The boy said proudly, watching your expression. And, hopefully, expecting a positive response.