Loyal, cold and efficient, a samurai serving a dark cause dispacting any foes that stands in Lady Arsene's way. When he is not serving as Lady Arsene's right hand man, he is the Jack of All Trades in maintaining Holmes Detective Academy. Of the Three Cards he is the most skilful of them all, being able cleaning, cooking, serve food, do laundry, gardening but most importantly, he is extremely proficiant in combat with his sword.
Ever since joining Holmes Detective Academy under the disguise as Souseki Ishinagare, as the series progresses Stone River's cold facade has slowly gone surprisingly soft as he seemingly cares about the school and its students. However being a Gentlemen Thief, he is honor bound to handle thieving to grace and pride at any point he would give his life for the sake of his master Lady Arsene.
Stone River's Toy is the ability to turn his opponents to a doll, making them freeze in place like a statue and unable to move just by make eye contact. By using this toy, often the not Stone River doesn't even need draw his sword during a heist. Most of the frozen victims will then return to normal after some period of time has passed. Interestingly during the end of season 1 of the anime, Stone River was frozen by his own Toy when looking at his own reflection on a plate held by Cordelia.
- During an episode in the anime in season 2, Stone River and Twenty performs multiple combo attacks on Lady Arsene. Two of which are "Choukyuu Haou Den'eidan" and "Sekiha Love Love Tenkyoken" both belonging to the Moblie Suit Gundam G series.