Okisaba/Oxaba feature the Tokyo Marui HK416D Akki Custom NGRS. Akki is an Japanese active airsoft player and has got various loadouts and gear that he features on his Twitter account. The base gun is probably the DEVGRU Custom variant inspired by US Navy SEAL's customized rifles, upgrades the HK platform with steel parts, enhanced stability, and realistic features like simulated recoil and magazine-empty stop.

Rio and Akki meetup for a Money Game battle organised by Airsoft97 and Maitri at the Libra Game Field in Ibaraki Prefecture. Held last 17 June 2018, this event was supported by different airsoft businesses and two big teams by Rio and Akki battle to collect the most money. Looks like it's something that can be adopted for your home fields if you're looking for variety.