Eiichiro Maruo (丸尾 栄一郎), also called Ei-chan by his friends, is the main protagonist of Baby Steps. He later becomes a member of Southern Tennis Club on his mother's suggestion to fulfill his lack of exercise. His current aim is to become a professional tennis player.
Eiichiro has an average stature for a tennis player. He has an odd hairstyle with short hair on the sides and spiked hair in the middle. He has a superior eyesight as compared to a normal person. After training hard for becoming a professional, he has muscled up a bit and his body has become totally tennis oriented.
He usually wears uniform at the school and tennis clothes at the club. Another noticeable feature is that he always carries a bundle of notes with him, be it for studying or for tennis.
Eiichiro has a perfectionist personality and is also called All-A, referring to his perfect grades. He tries to achieve perfection in every task that he performs, be it studies or tennis. He works very hard to achieve his goals to an extent that it even surprises his friends and tennis club members.
He is sometimes referred to as a high-school boy who sounds like an old man due to his habits of trying to do everything in order to be perfect.
Eiichiro initially starts playing tennis due to his concern over his health and wants to take some exercises. However, as he starts to participate in the tournaments, he starts to enjoy playing as well. This, then, leads him to decide to become a professional tennis player and works his way up to become one.Natsu Takasaki from class 2 appears to borrow his world history notes. After Natsu describes Ei-Chan as weird (as his notes look excessively perfect), she accidentally falls down and ruins his notes. After school, Kageyama invites him to the shougi club, but Eiichiro rejects him and explains that he wants to participate in some exercise. Upon arrival at home, his mother persuades him to visit the neighborhood tennis club, STC. At first he refuses to go, but his mother snaps and forces him to visit.
As he arrives at the STC, he is amazed by the size and facilities it consists. He notices Natsu playing tennis in one of the indoor tennis courts, but is discovered by Tajima. Yuuki immediately believes that he is spying on them and yells loudly, hence bring everyone's attention to Eiichiro. After being discovered, Natsu introduces him to the players of STC. He reluctantly joins the warm-up exercises which involves running 10 laps, 10 line touches, jump and dashing, 5 sets of side-steps, dashing, and etc. Unfortunately, Eiichiro collapses after doing all the exercises and is called pitiful by Tajima. Afterwards, he finds an excuse to leave, but is questioned by Natsu of whether studying is fun. Natsu reveals her intentions to become a professional tennis player, which causes Eiichiro to reflect on his life. When he was riding the bus home, he decides to get off half the journey and run back home. He later collapse again whilst running, and asks his mother to pick him up.
The next day, Natsu passes a message from Coach Morimoto, to him. He is invited to the STC again to practice playing tennis. After a few days, he decides to visit the tennis club again and successfully finishes the warm-up exercises without collapsing. Whilst waiting for coach Morimoto, Eiichiro decides to observe A court. He is introduced to Takuma Egawa who demonstrates a powerful serve which intimidates him. After Natsu teaches him the basic stance to hit the ball, he successfully hits a light serve from Takuma. After his successful hit, he begins to practice playing tennis, even though he is unable to produce the same shot. He also develops a Tennis Edition of his notes, just to feel the great sensation again, from his first successful shot.
Following his hours of practice he discovers Natsu and Takuma, and believes that they were dating. To his appreciation, he discovers that it was a misunderstanding. Soon after, Natsu finds him hiding in the bushes and she joins his tennis practice. As she leaves, Kageyama perceives that he likes Natsu, hence causing Eiichiro to feel flustered and confused. At home, he looks up at a dictionary for the definitions of like and love. The following evening, he spends approximately 6 hours practicing tennis. Even when Natsu calls his name, his concentration prevents his from realizing her. For the first time, Natsu says that Eiichiro will become a strong player, but Takuma shows his doubts.All-Japan Junior Tennis Tournament to his studies. The next day, Eiichiro goes to the STC, where Soji Ike comes and asks Eiichiro for a match.
Eiichiro accept his request, the match was hard for Eiichiro but he managed to score a point before Soji Staff comes and stops the match. Soji goes back to Florida leaving a big impact on Eiichiro. On the next day Eiichiro starts his long training to strengthen his body, mind and techniques.
Eiichiro decides to go pro and is looking for a way to become stronger in a short amount of time. He meets Coach Aoi who will be his future coach and the one who suggests to take a short-term study in Florida Tennis Academy. In Florida, Eiichiro meets a lot of people - from the staff of Florida Tennis Academy to the players who also aim to become a pro. Due to Ike's suggestion, he manages to play a lot of matches from these players. Initially, he experiences a "losing habit" which causes him to lose confidence. But due to Alex's words and the support of the staff, little by little, he manages to regain his confidence. Before the end of his short-term leave, he manages to defeat Alex, a professional player and gets the chance to play a practice match against Ike.
After a year of long hard training and tournaments, it's finally time for the All-Japan Junior. After he passes the first round with ease, it is time for his first challenge against Okada. After beating Okada, people start to acknowledge Eiichiro more. He also wins against Ogata in the quarter-finals. However, he lost against Kanda in the semi-finals, making him only part of top 4 of the tournament.
Having lost to Kanda and consequently, the All-Japan Junior, Eiichiro fulfills his promise to his parents - that he will give up on his dream of being a professional tennis player. However, based on his recent actions, some people, like Kageyama, are bothered by it. Even though he had a heart-to-heart conversation with Coach Aoi and Natsu, Eiichiro remains in deep thought regarding on what to do know in his future. Later, he learns through Coach Aoi that he has the chance to participate in All-Japan Championship Preliminaries due to the decision of the committee of Tennis Association to include the semi-finalists of All-Japan Junior as wildcards. He, then, decides to participate to the tournament after he manages to persuade his parents (through another set of conditions) and contacting the schools who offered him scholarships for college. He also obtains permission to train in America for 2 months after contacting his school to take a leave and Ike, who helped him find a part-time work in IMG Academy to cover his expenses.
Aside from reuniting with his friends in IMG Academy, he also meets Kanda who is also there to train and Pete Gonzales who initially a baseball player but switches to tennis when he reached high school. Like Eiichiro, Pete has good eyesight and reflexes. Aside from physical and mental conditioning, and practice matches in IMG Academy, Eiichiro also has vision training sessions, plays tennis at the beach and has become Ike's hitting partner. He also participates in Bradenton Open and defeats Pete in the first round. Before he returns to Japan, he defeats Kanda in a 5-set practice match and learns that Ike will participate in All-Japan Championship as well. 
Eiichiro and Natsu go to another date after Coach Aoi instructs Eiichiro to do what he wants to do and Natsu is on her day off after the tournament she played. During their date, they meet Onozawa who then introduces them to Yamaguchi, the All-Japan Championship's 10th seed, and Asano, a participant in the All-Japan Championship Preliminaries. Eiichiro also learns and supports Natsu's plan for her future as a tennis player. At the All-Japan Championship Preliminaries, he manages to defeat Konishi, Akimoto and Asano, thus, qualifies for the All-Japan Championship.
Eiichiro, together with Araya and Kanda, are now qualified to participate to All-Japan Championship. After Eiichiro defeats Tamakoshi in the first round, he faces Takuma in the second round. He thinks that if he loses to Takuma, he really has to give up his dream of becoming a pro and move on. Takuma initially gets the lead by winning the first set. However, after Eiichiro manages to hit Takuma's 230kph serve (which is considered to be one of the fastest serves) with a return ace, he breaks Takuma's service game, and leads him to win the second set. After an intense close match in the three-match set, Eiichiro emerges as the winner, which surprises the audience as Takuma is known to be one of the contenders in the tournament.
Now that Eiichiro defeated Takuma, Eiichiro starts to create a resume to attract sponsorship. He is now included in the Best 4 of the tournament after defeating Tanemura, and winning by default against Yoshimichi who withdraws in the tournament due to injury. However, he experiences an overwhelming defeat against the tournament's 2nd seed, Monma.
Eiichiro initially had very little athletic ability, but after working hard continuously to achieve perfection, he developed a higher stamina and more advanced tennis skills.
As a result of his trip to Florida, he picked up a routine that helps maintain a constant state of mind and consistent movement. Stated by himself, he seems to do well after fixing his strings and taking a deep breath.
One of Eiichiro's notable traits is his constant note taking. He is known for writing down his observations during matches in great detail, making probability charts for shot-selections, service placement and habits, as well as shot by shot replays of each point the games. This allows him to collect his thoughts and come up with strategy to beat his opponents.
According to many tennis players and coaches, Eiichiro's hitting form is perfect. This is because he used to practice his form by hitting against the wall and wrote down how he needed to adjust his body to create an ideal swing. Eiichiro's mastery of the basics is the foundation of his all-court style, using a variety of basic shots to win points.
Eiichiro's eyesight is noted to be extraordinary, being able to follow the trajectory of fast balls. Even during his beginner days, Eiichiro was able to see all of Takuma's serves clearly and see their path. It is due to his superior vision and the ability to distinguish it at such high speeds. Later, he becomes able to use his eyesight to look at the opponent's body along with his analysis of his opponent in order to predict where the ball will go.
He further improves on his eyes with a training regiment when he goes to Florida again after the All-Japan Junior high tournament.
Eiichiro has developed a great control over his shots and can hit with a very high accuracy to any part of the court. He starts with using a 9 square division, but has increased its accuracy to 81 square division.
After his match with Takuma, he realizes that he needs a fast serve in order to keep the flow of game with him before starting a rally using control skills. He copies the movements of Takuma in order to learn a fast serve. Coach Aoi helps Eiichiro to train various muscles to utilize a fast serve.
Tennis Oriented Body
After deciding to focus his whole year to his goal of winning the Nationals and becoming a pro, Eiichiro practiced with the coach regularly, using many different routines.This helped him break his body and develop it into a body which is totally aimed for tennis.
Visualizing a Winning Vision
During the Kantou match against Nabae, Eiichiro devises an array of strategical attack patterns that pierced through Nabae's formidable defenses. During the All-Japan Championship tournament, he does extremely well by carefully scripting his scenarios against Tamakoshi who is a pro. Tamakoshi is exceedingly confused during the match, and thought that he was unable to perform well because he was not allowed to by Eiichiro.
Although they attend the same school, Eiichiro and Natsu do not really know about each other in the beginning. Their first encounter was when Natsu's friend recommended her to borrow study notes from Eiichiro, which she accidentally ruins. After being encouraged by his mother to participate in some sports, Eiichiro decides to try playing tennis at the Southern Tennis Club. He meets Natsu there and learns for her aspiration to become a professional tennis player. As he gradually devotes his life to playing tennis, his friendship with Natsu grows and he noticeably falls in love with her. The day before the start of Kantou Junior Tennis Tournament, both of them confess their feelings for each other and become a couple. They have also met each other's parents and has a good relationship since then. They also go on dates during their free time and their first kiss was before Eiichiro's match against Kanda.
Eiichiro and Takuma are on fairly friendly terms. Eiichiro admires Takuma and his superior tennis abilities, and he is currently aiming to be as good as him. Before Eiichiro's first official match against Takuma, Eiichiro believes that he has to defeat Takuma in order to pursue his dream. It is due to Takuma that he manages to reach his current state because of the things he learns from Takuma.
- Likes simmered pumpkin (カボチャの煮物, Kabocha no Nimono) and cleaning
- Not very good at cooking 
- Before he started tennis, he used to do the following: 
- Studied swimming (1 - 3 years old)
- Studied piano (5 - 6 years old)
- Studied calligraphy (6 - 11 years old)
- Went to cramming school (14 - 16 years old)