|Name (kanji/kana):||鮫島 力|
|Localized Name(s)|| Jack|
Riki Samejima (鮫島 力, Samejima Riki) is the guardian 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 and is never seen smiling during any of his animations (Kunio is seen grinning in his dashing animation while Riki is not).
- In Renegade, Riki is known as Jack.
- In 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 name Ryan.
- In Crash 'n the Boys: Street Challenge, Riki was named Crush, a member of Team Thornley, who replaces a black character named Raphael.
- In River City Ransom Underground Ryan's full name was Ryan Samejima.
- 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 bares a close resemblance to him due to his Pompadour hairstyle and his uniform color.
- Riki's birthday is on May 5.
- Although never referred as such, Riki can be considered Hanazono High's Banchō (番長), a japanese term used to call the leader of a juvenile delinquent gang.This can be noticed specially in Nekketsu Kōha Kunio-kun where he's the 2nd stage boss, and in several of the sports games he's the de facto captain of Hanazono's team. Also he's the rival of Kunio, who is considered the leader of the Nekketsu High gang more often than not.
- Ironically, in River City Ransom he's part of Nekketsu High due to Riki being the playable character for the Player 2 position.
- Riki is the only character in the franchise who has been given an official surname (Samemija).