Hikaru lives within the Old City all throughout her life. The history of her parents and the relationship they had with her is unknown. It is assumed that Hikaru did not have any relations with any individual until she met Alyssa. They became friends when Alyssa sought her guidance and skill. After a few days, the two newly found friends called one another "Scarf Buddies" due to both wearing scarves.
Hikaru consistently taught her friend that survival is key in this new world. She implies that killing is reasonable if one gains from it, and to avoid wasting ammunition and energy for others. She also made mention of her rival, a fellow sniper within the Old City that has far more skill than she does. However, she lied from spite and jealousy and said that this rival of hers has far less accuracy and can be defeated easily.
When Alyssa had told Hikaru that she wanted to enter Crestfall, she obliged by her wish. They both set off toward the deadly Highway, and prepare all day to survey and scan the area. Hikaru was crystal clear in her advice and teachings about both the Faded hordes and the Crestfall guards. This was the moment that Hikaru trained Alyssa to be more coordinated in her attacks and defensive maneuvers. In a few hours, they both decided it was time and charged for the gates.
Eventually, they did reach the gates in which armies could not ever fathom in accomplishing. Unfortunately, the Crestfall guards took notice of the two teenage girls and blasted Hikaru off the overpass on the Highway. Hikaru lay motionless on the street below in a pool of her own blood, and nearly lost her limbs. Alyssa looked down a single time, yelled out her name, and simply gave up in tears.