Arbachakov was phenomenal during his prime, beautiful to watch. I doubt he took advantage of the day before weigh in as much as the bigger Nakatani did, so he'd be the lighter, smaller man in the ring, however Junto was pretty inexperienced at world level when he left Fly. On balance, assuming the fight is at 112lbs, I'll go with the smaller, but more talented, Yuri.
Yury by decision, because prime Junto Nakatani is more at 115-118 lbs and currently at 122 lbs. And the defense of Yury Arbachakov prime was very exceptional in Flyweight.
Another vote for Arbachakov. Nakatani is awesome but at Flyweight I don't think he was on the same level as a prime Arbachakov.