Here's her story:
''Aika—“Sailor Star Singer” is Usagi and Seiya’s second child. She was born not too long after they started their travels. Because her family is rather nomadic and adventurous, Aika is used to living a carefree lifestyle. She is definitely more tomboyish than her elder sister, and her constant cheerfulness can sometimes bulldoze and overwhelm others to exhaustion. She can also have a quick temper but forgets grudges easily.
When Aika awakens as a Sailor Star Singer, she chooses to live on Kinmoku. There, she befriends and becomes close with Ami and Taiki’s daughter, and fellow senshi, Sailor Star Seeker. (eventually she will also gain the ability to switch genders at will). Despite her new role as one of Kinmoku’s Starlights, Aika still gets bouts of wanderlust now and then, and is considered untamable by a lot of friends. Aika’s name means “love song.”!"