Hikaru Kamiki/Plot

History
Much of Hikaru's past remains a mystery. According to Akane Kurokawa's research, he was once an aspiring actor who joined the Lalalie Theatrical Company when he was 10 years old. When he was 11, however, he somehow got into an affair with actress Airi Himekawa, who was already a married adult at the time, impregnating her with Taiki. At some point afterward, Airi's husband, Seijuurou Uehara, learned of the affair and subsequently committed murder-suicide with her. Since only Airi and himself knew about the affair, Akane theorized that Hikaru leaked that information to have her killed without leaving any incriminating evidence.

Hikaru continued studying at Lalalie for the next 4 years. When he was 15, his affiliation with the company led him to meet a 16-year-old Ai Hoshino, who was taking acting lessons there to start her idol career. The two subsequently began a secret relationship, even sleeping together, before breaking up at some point. Afterward, through unknown means, Hikaru learned that he had impregnated Ai with Aquamarine and Ruby during their relationship. Since only he, Ai, and Ichigo Saitou could have known about the pregnancy, Aqua would later theorize that he tracked down the hospital where Ai would secretly give birth and leaked this information to Ryosuke in hopes that the obsessive fan would kill her before she gave birth.

Upon turning 16, Hikaru suddenly left Lalalie and went on to instead graduate from a normal science course. When he was 25, however, he suddenly returned to the entertainment world by founding his own talent agency. From there, he eventually went on to meet popular actress Yura Katayose, whom he became drinking buddies with.

Prologue
Ai Hoshino contacted Hikaru roughly a week before her birthday, asking him to meet Aqua and Ruby after overhearing them talking about their father. It was implied that Ai gave him her new address.

Following Ai's death at the hands of Ryosuke, Aquamarine deduced that the otherwise ordinary college student could not possibly have figured out her secret address. Since the other people who knew this information did not have any real motive to have Ai killed, this caused Aqua to conclude that Hikaru leaked her location to have her killed off whilst leaving no traces back to him.

Private
Before going to Miyazaki for the B-Komachi music video shoot, Ruby Hoshino paid her respect to Ai Hoshino's grave, and Hikaru passed by her, muttering to himself about how beautiful Ruby has grown. He then stood in front of Ai's grave and affirmed that she grew to be beautiful because she was his and Ai's child.

The Main Story
During the Japan Film Awards event, Hikaru passed by Akane Kurokawa, and Akane almost mistook him as Aqua.

Movie
Hikaru appeared as a drinking buddy to actress Yura Katayose, referred to as "Miki-san", and listened to her rant regarding her work offer declining due to her getting older. She also revealed to him that she would take a month off to go hiking in a mountain, and Hikaru warned her to watch her step. Later on, Hikaru stood over Yura's dying body, implied to be pushed off by him, and taunted her for not "watching her step".