The Meeting of the Golden PairEdit
The Golden Pair met in their first year at Seigaku. In the anime, Eiji was a flashy singles player and found Oishi's play style boring. When he challenged Oishi to a match, he lost and couldn't figure out why. Retreating to the green bins at the park - a place the Golden Pair always go to when they need to think things over after losing a match - he saw Oishi practicing there. Eiji then told Oishi he would play doubles with him until he was able to defeat Oishi at tennis. In the manga, Eiji met Oishi by bumping into him in his first day of school after Shūsuke told Eiji that Oishi was a nice person, then developed quickly a strong admiration towards him (he even defended Oishi when he found some teammates spreading ill rumors about him), and finally asked Oishi to be his partner. In the anime, when Eiji is first introduced, he launches into a full description of himself. "My name is Kikumaru Eiji. I am twelve years old. I was born on the 28th of November. My blood type is A. I have a grandma, grandpa, Mother, Father and two older brothers and two older sisters...."
The Break UpEdit
Eiji has a terrific personality and he loves to tease others as well, which caused Oishi, who is a really sensitive person to get really mad in one occasion and caused the biggest crisis of Seigaku - the breaking up of the Golden Pair.
In the rematch against Hyotei in Prince of Tennis OVA Episode 12, Kikumaru Eiji and Shuichiro Oishi went against Ryō Shishido and Chōtarō Ōtori, who were using the Pile Mirage, a formation where Shishido is in front of Chotaro. Seigaku Golden Pair's harmony is destroyed by that formation, at least until the score went to a match point with Hyotei in the lead, the score set at 6-3. Suddenly, in the current situation of absolute pinch, the Golden Pair's harmony change. The pair remember their past, their matches, their friendship and everything that happened to them. Then, a thin aura starts spreading around the Golden Pair's bodies. Their eyes change color into gold. They synchronized, as what Keigo Atobe's Insight could tell. Without eye contact or call they can hit heavy shots due to their absolute trust in each other, even their breathing being synchronized. According to coaches, Top Pro doubles say that you can't become the double's world champion without that kind of synchronization. Glden Pair catch up until the tie-break score is 6-6 then 7-6 with Seigaku leading. In the service game of Hyotei, Otori uses the scud serve despite knowing that the burden it puts on his previously injuried arm may seriously hurt him. The momentum went back to Hyotei. In next rally, when Shishido returns the ball, the Golden Pair is ready to smash it. However, the match ends with the win of Hyotei pair, due to Kikumaru not letting Oishi hit the ball. Side viewers speculate that thanks to synchronization, Kikumaru also sensed the limit of his partner's wrist, and that hitting the ball in current condition would re-injure it. It seems that when they were synchronized, the pair was unconscious. They don't know what happened after the moment of their synchronization.
While they are rested during the semi-finals, in the finals against Rikkai they are shown to have mastered control over synchro, making them the first and, during the time of the Nationals, the only middle-school pair to achieve such skill.