Remember what Gansu Burger owner (I forgot his name, damn) says in chapter 3;
Once every 3 years, on the night at, 8 April, there will always be a missing person after fall onto the sea of Kumine town. And you wondering where they gone to? They probably gone slipped through the timeline to the past, by accident, and the burger owner is one of 'em. The burger owner had probably went through from 2016 to 1994 (considering he had opened his burger restaurant in this era for 6 years). In the original 2000 timeline, the burger owner was supposed to be around middle school age. But in this alternate timeline, he's apparently a grown up man from the future now. So expected, another time traveler spotted. That's why I frankly feel something odd about Wagatsuma appearance. Since Gaku was from 2022, Wagatsuma must be from 2019 🧐.. OH WAIT, WAGATSUMA APPEAR IN THIS TIMELINE SINCE HE WAS CHILD, SO HOW THE HELL HE ACCIDENTALY WENT BACK TO THIS TIME WHEN HE WAS STILL A KID AND WHAT YEAR DID WAGATSUMA TIME SLIPPED!? STAY TUNED FOR MORE CHAPTER & HOPE IT'LL GIVE AN ANSWER