Masumi is an expert at Speed Adventure. He was able to adopt the title of a treasure hunter from his techniques of searching ruins and excavation, but he's not as good as Akashi. In episode 1, after taking the Heart of Gordom, he briefly returns his Accellular to Satoru, who in turn threatened him to drop him into red-hot magma for it if he did not accept it again. Masumi vowed to be better than Akashi. Natsuki is quite close to him after he found her with debris on top of her in a cave where flowers grown in a barren area. She made him quite jealous when she got close to Shouta. He acutally has encountered Yaiba of Darkness of the Dark Shadow clan before hand. In Episode 9, it is revealed that when Masumi was a child, he was part of an abusive excavation group that Yaiba killed them all. Masumi has since wanted to seek revenge. In Episode 21, he did not particularly get along with Eiji and they had to work together when Akashi assigns them together to get the precious Mallet of Luck. Masumi really impressed Quester Rei in episode 28 in his resilience in obtaining the Legendary Armor they were after. In Episode 33, Masumi and Natsuki was kidnapped by the Questers to take them where he found her. Once Natsuki discovered she was the last of the Lemuria Civilization and consumed by the Sun of Lemuria, Masumi was the one able to break her out of it. Later in Episode 46, Yaiba tried to use Masumi to power the Precious called the Three-Headed Dragon of Darkness to engulf the world with darkness. It was about the same time that Masumi found a diary that he wrote during his anger in the first episode and wanting to surpass Akashi as the best adventurer. A dangerous new Jakuryuu gave Masumi a reason to surpass Akashi so he challanges him to a duel that he can defeat the Jakuryuu which Akashi agrees to. Akashi ultimately takes the monster down. Yaiba convinced Masumi that he had darkness in him. He saw the power of the Precious when he punched Ryuwon with extraneous force. Masumi let Yaida get to him to the point of bringing forth darkness from outer space toward the Earth. Watching the other Boukengers in harm, Mausmi brings forth light within himself to defeat Yaiba. But it is Yaiba's last words about Masumi still having darkness within and what harm he could cause to his teammates, Masumi leaves the team much to their sorrow. He wandered around brooding and was approached by a mysterious girl. When the city was under attack by Kraths and rain, Masumi reunited with Natsuki and she reminded him that he was the one who encouraged her to continue on. She told him that his real treasure was being an adventurer. He was surprised to hear that Akashi was dead and Natsuki commented on how he didn't have to worry about suprassing him anymore. He thought of that and then came to rescue the Boukenger when Desperado attacked them in front of SGS headquarters for the Brain of Gordom. He stated that his treasure was focusing on his light side more than the dark side. He endlessly used the Dual Crasher to defeat Desperado and did so with his friends except for Akashi. Akashi returned and had survived, he traveled to outer space and Masumi became the chief, continuing in adventures wiuth Natsuki, Eiji, Souta, Zuuban, and the rest of SGS.