Once a shinobi from the Land of Snow, Gekkō worked closely with Ryōgi's father on missions. Ultimately, however, he wanted more and formed the Byakuya Gang, gathering allies under the false veil of helping the less-fortunate while steadily building up his own personal fortune. Realising Ryōgi's potential power, Gekkō killed the young boy's parents and altered his memories, making him think that Gekkō saved him from his parents' attacker. He then swayed Ryōgi into joining the Byakuya Gang, claiming that his father was also a part of it.
Seemingly, Gekkō was once a noble and loyal man to his country and friends, but ultimately became selfish and amoral. Proving to be very manipulative and sadistic, he formed the Byakuya Gang all around a lie in the hopes of enriching his own life. He had no qualms about sacrificing his allies and best friends, even killing them to keep more for himself and cover up loose ends.
Gekkō is a very effective leader and strategist, having skilfully gathered a number of followers and designing various heists for the exploits of the Byakuya Gang. His greatest strength is his deceptive nature. Showing a strong aptitude for genjutsu, Gekkō is able to warp people's perspectives and re-write their memories. He also makes use of mirrors and reflections to put people under genjutsu by either controlling them, or causing them to look away, if they know how his jutsu works, and therefore giving himself an opening to take further action.
Byakuya Gang Arc
Main article: Byakuya Gang Arc
Gekkō and his gang's exploits eventually made their way to Konohagakure. Starting with small heists, Gekkō steadily worked his gang around the village to spread their word of equality for all. Their exploits ultimately gained support from many in the village. This ultimately allowed Gekkō to spread false rumours of various legit companies being unfair to their workers. As this caused a mob to spread, making the Konoha-nin focus their efforts on calming the angered villagers, it allowed Gekkō to set his sights on Katasuke Tōno's scientific research.
While making his way out of the village, Gekkō killed one of them, who was driving the train, but Ryōgi, who he sent to fend off the pursing Boruto Uzumaki and Shikadai Nara, failed in defeating them. Ultimately, however, his efforts failed as Naruto Uzumaki arrived and quickly subdued him. Gekkō was then captured and sent to prison.