The protagonist of the series, Ryoma is the son of Nanjiro Echizen, who was formerly known as "Samurai Nanjiro" during his days as a professional tennis player. Ryoma gains the nickname "Samurai Junior" later in the series. He makes his first appearance when he criticizes a high school student about his tennis knowledge in a subway. He always says: "Mada Mada Dane" which means in English is "You still have lots more to work on." Ryoma Echizen is voiced by Junko Minagawa (Japanese Version) and by Neil von Black (US Version).

Four years prior to the start of the series, Inui and Renji Yanagi from Rikkaidai were an unstoppable Elementary School Doubles Pairing. Unfortunately, their doubles pairing was ended when Yanagi suddenly moved to the Kanagawa Prefecture.

Inui is a highly intelligent player. He plays what he calls "Data Tennis," which involves collecting and analysing data for a player in order to determine weaknesses. He is even able to determine the exact probability of certain shots being successful. The Data Tennis style actually originated from Yanagi. To his surprise, Data Tennis does not work against Ryoma Echizen who evolves over the course of a match, and Jin Akutsu (although Inui never played against him), due to his natural flexibility making shots unpredictable. Inui also finds it difficult to get accurate data on Shusuke Fuji and Kunimitsu Tezuka. Before Echizen came to Seigaku, Inui was considered the third strongest player of the team, with only Tezuka and Fuji above him.

Inui was beaten by Ryoma, and then lost to Kaoru Kaidoh (who had also been beaten earlier by Echizen and was determined not to lose his spot) at the beginning of the series and became the team's manager. He uses his data to create exercise programs for the team. His most hated innovation would have to be his "Inui Juice" or "Penal Tea" (penalty), a disgusting health drink which is used as punishment. The contents of "Inui Juice" are unknown, but Inui is always coming up with new and "better" recipes. When the team went bowling, Inui's new invention "Aozu" first knocked out Kaido and even Fuji (who usually enjoyed drinking the "Inui Juice" or "Penal Tea") as well as the rest of the team. Even Inui himself falls victim to the "Aozu".

Eventually, Inui is able to make it back as a regular by using the data he obtained over the time he was manager, losing to Kunimitsu Tezuka but beating Takeshi Momoshiro. While he's a very good singles player, he usually plays doubles with various partners, most notably his protegé Kaoru Kaidoh. His doubling with Kaido helped Seigaku overcome their problems with doubles teams (which Ryuzaki considered weak with only the Golden Pair as an effective team).

Momoshiro is known as Seigaku’s number one rascal. He really wants to be liked by everyone, which is evident by his preference to be called "Momo-chan," even by the freshmen. As a compromise, some of the freshman call him "Momo-chan-senpai" while the third years call him by "Momo."

At the beginning of the series, he played an unfinished match with Ryoma Echizen (he did this to see the twist serve), though Momoshiro was injured at the time. Later, they become best friends and even doubles partners for once. Momoshiro's signature move is the "Dunk Smash," a very powerful response to lobs as he leaps several feet into the air, which he likes to finish off saying, "Don," upon landing. He later develops the "Jack Knife," a strong backhand shot.

Momoshiro is an aggressive baseliner. For a short time, he is cut from the regulars, after losing to Inui and Tezuka during Seigaku's 2nd monthly ranking matches. He takes being cut pretty hard and doesn't show up to practices for three days, leading the first years to think that Momoshiro has quit the club. Instead of going to practice, he spent his time playing street tennis; however, as he plays a match with An Tachibana, a good friend of his, he realizes his flaws as a tennis player and that in order for him to become stronger, he needs to stop underestimating his opponents. It is during this time that Momoshiro's importance to Seigaku as a team is revealed.

As the player who is the most open and friendly with everyone, Momoshiro is connected to everyone on the team on some level. And as such, he's one of the few members on the team that everyone seems to care about, which is why his disappearance affects all the regulars in some way. Momoshiro being cut from the team even leads to the temporary break up of the Golden Pair and even Eiji notes how practices are not the same without Momoshiro around. Although Ryoma, in particular, seems unconcerned about Momoshiro being cut from the team, in reality, he is worried about Momoshiro and goes looking for him during lunch period; a moment that reveals both how important Momoshiro's friendship is to Ryoma and how important Momoshiro is to Seigaku. Thus, when Momoshiro returns to practices, all seems right with the team again, although Tezuka punishes him for missing practice by making him run a record high of 100 laps. This is also when Momoshiro as a character is revealed in that Momoshiro doesn't worry about taking himself too seriously and despite being cut from the team, he is determined to support and cheer his teammates on as they face Hyotei in the Regionals.

Yet, Momoshiro ends up having to play a serious part again, almost instantly, when Oishi gets injured and doesn't show up for the match against Hyotei. Momoshiro's character is further revealed as he shows courage by first attempting to relieve Oishi from the hospital as quickly as possible and then, by being the one to take Oishi's place as Eiji's partner. Up until this point, Momoshiro is still a novice at playing doubles. But in one of Momoshiro's finest moments, he not only helps Eiji win the match against Hyotei, but takes the opportunity to master doubles with Oishi's quickly-given advice. Spectators even said Momoshiro and Eiji playing was like watching the Golden Pair. Momoshiro shows that he is not only one of the most adaptable people in Seigaku, but he's also a player and a friend who always gives 100% and comes through for his teammates. Even Inui has noted that Momoshiro's ability to overcome hurdles is amazing. He then is able to remain as Regular on the team when Tezuka has to leave the team to recuperate from his injury from his match with Hyotei's Atobe.

As Momoshiro is the closest to a true friend Ryoma Echizen can claim, the two spend much time together eating hamburgers or playing street tennis. Unlike Ryoma, who is absolutely clueless as a doubles player, Momoshiro develops an affinity for playing doubles and even masters it, despite expressing a preference for singles. Momoshiro is good at "faking out" his opponents, and can be extremely sly and tricky on the courts. His ability to read the opponent's movements and to observe their viewpoints and expression allow Momoshiro to read his opponent's mind, thus he is able to guess where the ball will go and use shots that will confuse his opponents; however, it's an ability that Momoshiro, himself, hasn't noticed yet. Kunimitsu Tezuka, arguably one of the best tennis players in the middle-school circuit, has commented that when Momoshiro realizes his true potential as a tennis player, he'll be an extremely formidable and troublesome opponent.

During the Inter-school ranking tournament, before the National tournament, Momoshiro and Echizen played a singles match to determine who'll be a regular. Unfortunately, after Momoshiro was leading 4-0, Echizen decided to forfeit the game and Momoshiro was angry at him for not taking this match seriously. Eventually, Momoshiro finally realised that Echizen really wanted to take part in the US Open even though Echizen said he would attend the Nationals with the regulars. They then played a friendly singles game, despite Momoshiro losing 6-2, his friendship with Echizen has been the most valuable ever since their first encounter.

Before the National tournament, Momoshiro trained in the mountains, and as a result of his training he improved upon his natural "insight". While similar to Atobe Keigo's ability to see the weakness or potential of another player, Momoshiro's time in the mountains caused his insight to be related with nature, ex: the position of the sun, the direction of the wind, stray stones to deflect serves, etc.

Momoshiro and Kaoru Kaidoh are eternal rivals, and constantly try to out-do each other. Surprisingly enough, this makes them efficient as a doubles pair, because the two rivals know each other so well. In Genius 379, the last chapter of the manga, Momoshiro is seen as a third year and the new sub-captain of Seigaku, with Kaidoh as his captain. Their rivalry has, apparently, somewhat mellowed with time