Riki (りき Riki) is the banchō of Hanazono High School and the second most recurring character in Kunio-kun series. He first appears in Nekketsu Kōha Kunio-kun as the first stage boss. He is the eternal rival of Kunio, with whom he shares many traits such as his roughed up appearance and his deep sense of honor. Unlike his rival, however, he has a more serious, quiet and down-to-business personality, as noticed in Shin Nekketsu Kōha: Kunio-tachi no Banka where he's the character that speaks the least.
In the Downtown Nekketsu series his full name is Riki Samejima (鮫島力 Samejima Riki, さめじま りき Samejima Riki).
Riki serves as the boss of the first round of the game. He is known as "Mach Punch Riki" because he's one of the fastest punchers in Japan (and in the game).
In this game, he is named 雲雀力, Hibari Riki (ひばり りき, Hibari Riki). After this game, he was simply known as Riki until the release of Downtown Nekketsu Monogatari, where he is named Samejima Riki.
Riki serves as the team captain of the Hanazono High School Dodgeball Team. His team serves as the first opponent for Nekketsu High school, lead by Kunio, in the World Tour mode.
According to Kishimoto, Riki formed a dodge ball club in Hanazono High School the instant he heard that Kunio had joined such a club.
When Ryūji and Ryūichi Hattori start taking over local high schools, Riki initially has no interest in the matter. But one day, his girlfriend Mami is kidnapped and he receives a letter from Reihou Academy. Enraged, he prepares to storm Reihou Academy and rescue his girlfriend, but he has an unexpected encounter with Kunio just as he leaves the high school. Kunio, having heard what happened to Mami, offers his help, which Riki begrudgingly accepts.
Riki and Kunio manage to fight their way across the city to Reihou Academy, defeating the students of the many high schools under Reihou's control that try to stop them. They defeat Ryūji and Ryūichi and successfully save Mami. However, it's revealed that the true mastermind behind the whole thing is Kunio's former schoolmate, Taiki Yamada. Riki and Kunio manage to defeat Yamada and break Reihou Academy's hold over the other schools.
In the EX Remake of the game, Riki starts with the Mach Punch/Stone Hands technique, calling back to his first appearance as "Mach Punch Riki." If you're playing as Riki alone, he will outright reject Kunio's help, and Kunio will challenge Riki to a sparring match after exiting the Kobayashi Industrial Factory Site. If you're playing as Kunio alone, the roles are reversed.
Hanazono Town is being threatened by the recent arrival of Munataka Industries. The chairman's only son, Yūji Munataka has taken control of various schools and has been terrorizing the neighboring areas, including the local high school. As the school's banchō, Riki has had enough. When Hiroshi is beaten up by Yūji's men, Kunio decides to put a stop to Yūji, thus Kunio and Riki join forces once again. They proceed through the town and reach the top floor of the industries, beat Yūji in a fight and then drag him to the hospital to apologize to Hiroshi.
Gameplay-wise, Riki plays identically to Kunio. He can only be used by the second player.
Riki makes an appearance in the period play as Rikigorō.
In the two player mode of the game, Kunio runs into Riki in Umeda when Nekketsu High School takes a class trip to Osaka. As it turns out, Hanazona High School also took a class trip to Osaka, and they were staying in the same hotel, which allows Kunio and Riki to work together. In one player mode, Riki doesn't appear.
- In Renegade, Riki was changed to a character named Jack, who bears a resemblance to Luther from the seventies film The Warriors.
- In the NES version of Super Dodge Ball, he is also known as Jack, a captain of Team Pro All-Star.
- In River City Ransom, Riki was renamed Ryan.
- In Crash 'n the Boys: Street Challenge, Riki was renamed Crusher (shortened to Crush in-game), a member of Team Thornley, who replaces the character named Raphael in the original game.
- In River City Ransom: Underground, Ryan's full name is shown as Ryan Samejima in the school's year book on the file select screen.
- His nickname is "Mach Punch Riki". The inspiration for the Mach Punch comes from the Speed Racer manga (which was known as Mach GoGoGo in Japan). Animating the Mach Punch in the original arcade game (when Riki grabs Kunio and punches him) reminded Kishimoto of the Mach GoGoGo anime.
- Riki has a height of 180 cm.
- According to Yoshihisa Kishimoto, Riki's name originates from a notorious yakuza.
- Riki has had at least two confirmed girlfriends in the games: Mami in Downtown Nekketsu series, and Kyoko in Kunio-tachi no Banka.
- The character Kazuma Kuwabara from the anime Yu Yu Hakusho bears a close resemblance to him due to his Pompadour hairstyle and his uniform color.
- In Nekketsu Kōha Kunio-kun, Riki's surname was Hibari. Samejima was introduced as his surname in Downtown Nekketsu Monogatari. However, according to Yoshihisa Kishimoto, Riki is simply named Riki, just like the rest of the characters that debuted in Nekketsu Kōha Kunio-kun (Wataru is one exception). It is unknown if Riki is his surname or given name.
- Kunio's catchphrase, "Namen'nayo!" (なめんなよ!, roughly translates to "Don't mess with me!"), originated from Riki in the original arcade game as well as in the Famicom version. He originally said "Namen'nayo kono yarou!" (なめんなよ この やろう!, roughly translates to "Don't mess with me, punk!").