Arii made his professional debut against Yuki Hamada at RISE WORLD SERIES 2019 Semi Final Round on July 21, 2019. He won the fight by unanimous decision. Arii next faced Lehe at ONE Warrior Series 8 on October 5, 2019. He won the fight by a third-round technical knockout, due to doctor stoppage. Arii faced the unbeaten Ryoga Terayama in his third and final fight of the year at Stand up vol.1 on December 22, 2019. The fight was ruled a unanimous decision draw, with scores of 29–29 across the board.
