Riki Samejima (鮫島 力) is the the second most recurring character in Nekketsu Kouha Kunio-kun.
- Hair Color: Blue
- Eye Color: Blue
- Height: 180 cm (5'9" ft)
- Weight: 80 kg (176 lbs)
- Blood Type: O (Unknown in Nekketsu Kakutou Densetsu)
- Status: Alive
- Affiliation: Hanazono High School (Cross Town High School in River City Ransom), Team Thornley (Crash 'n the Boys: Street Challenge)
- Year: Senior (held back one year)
- Alternate Names: Jack (Renegade, Super Dodge Ball), Ryan (River City Ransom games), Crusher (Crash 'n the Boys: Street Challenge)
Riki is a 3rd year student and the banchou (delinquent leader) of Hanazono High School. He is Kunio's rival and best friend, and like him he takes the role of helper in various sport clubs at his school, which grants him praise from his peers and juniors at the school. He is known as "Mach Punch Riki", and just like Kunio, is a righteous delinquent who fights for justice. However, when his anger reaches the boiling point, he snaps and goes berserk.
His first appearance in the franchise is in Nekketsu Kouha Kunio-kun as the first stage boss. In Downtown Nekketsu Monogatari, Riki and Kunio join forces for the first time and become best friends. In his subsequent appearances in the franchise he would face Kunio in different sport competitions (Downtown Nekketsu Koushinkyoku: Soreyuke Daiundoukai and Bikkuri Nekketsu Shin Kiroku! Harukanaru Kin Medal) or become his ally (Shodai Nekketsu Kouha Kunio-kun and Shin Nekketsu Kouha: Kunio-tachi no Banka).
Before becoming the banchou of Hanazono High School, Riki was the ace of his school's soccer club. The biker gang Mushamonzen attacked members of the club, and Riki built his legend as "Mach Punch Riki" by destroying the biker gang in revenge and taking the position of banchou from Sakata. However, this came at the cost that he was not only removed from his school's soccer club, but he was forced to repeat his senior year. Soon after, he had his first encounter with Kunio and was defeated.
In the Downtown Nekketsu series his full name is Samejima Riki (鮫島力, 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.
In Renegade, Riki is changed into a character named Jack. The character bears a resemblance to Luther from the seventies film The Warriors.
- 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.
- According to Yoshihisa Kishimoto, Riki's name originates from a notorious yakuza in his youth.
- 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 Kouha 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 Kouha 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!").
- Riki shares many traits with Kunio, 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 Kouha: Kunio-tachi no Banka where he's the character that speaks the least.