Sonoko Ijuuin was the captain of the softball team at Juuban Municipal High School, and the number one fan in the Three Lights Fan Club. She was also the human identity of the Phage known as Sailor Leaguer.

In episode 187, Sonoko became jealous of the attention Seiya was paying to Usagi, a girl Sonoko considered to be beneath him. She made a bet with him, saying that if her team could beat his at the upcoming school softball game, he would no longer be allowed to associate with Usagi.

When the game was temporarily delayed due to rain, Sonoko sought out Usagi and declared her intention to hit the ball directly toward the other girl. When Usagi admitted that she knew she probably would not be able to catch it, but still insisted that she intended to do her best and not give up, Sonoko was impressed with her spirit.

After Sailor Lead Crow took her Star Seed, Sonoko turned into a Phage, but was saved by Eternal Sailor Moon.