Aqua Hoshino

"The guy who made Ai go through such a thing is in the entertainment world. Since that guy is related to me by blood, I can track him through genetic testing with a piece of hair. I can't die yet. Not until I find him... and kill him with my very own hands."

Aquamarine Hoshino, or more commonly known by his stage name Aqua (アクア), is the titular main protagonist of the Oshi no Ko manga series. Aqua was previously known as Gorou Amemiya, a medical doctor who treated patients. He developed an obsession with idols (specifically for Ai Hoshino, a member of the defunct idol group, B-Komachi) after encountering Sarina Tendoji, one of his patients holding the same infatuation. He was reincarnated along with his twin sister Ruby Hoshino, also formerly known as Sarina, and is now the child of Ai.

In Aqua's new life, although dumbfounded by the situation, he enjoyed being Ai's child. His wit and conversational skills while a child disturbed various people but had some benefits as award-winning director Taishi Gotanda swiftly praised him for how much he talked. These skills greatly serve him throughout his childhood, and even to the present. Aqua also enjoyed a privileged life. He lived luxuriously due to being a child of a famous idol, and he enjoyed watching his mother perform. A good life which, unfortunately, ends after a deranged fan of Ai commits a terrible atrocity towards his family.

This event would fundamentally change Aqua. He swore he'd do anything to find whoever was behind the tragedy. Despite numerous years passing, he is unrelenting in his goal, unlike his sister. Many of his actions were driven by this very ambition. He is willing to do anything to get closer to the truth including committing acts that teeter incredibly delicate lines.

Appearance
Aqua has blonde hair and is relatively tall. He has blue Aquamarine eyes, which is what his mother named him after. He often changes his appearance due to his job as an actor. He is described as "handsome" and features a star in his right eye; symbolizing that he and his sister are halves of their mother. When he was a child, he was often called cute by those around him.

Due to him being Ai's son, many people were able to point out their similarities despite being unaware of his pedigree. Much to Aqua's dismay; as, prior to Chapter 105, he wanted to keep the truth about his late mother from being known to the general public.

Personality
Before the tragedy that struck his family, Aqua was considered relatively normal other than his unparalleled prodigious talent in acting even as a child and his quick wit and intelligence. With him retaining his past experiences, he accomplished many things not expected for someone his age. Performing acting jobs was something he was open to and excelled at.

After the tragedy, he transformed. -- becoming cold, calculated, cunning, and discreet; A man willing to do whatever means necessary to see his goals through. The pain he underwent tends to resurface anytime he seems to forget his goals. This is the case when Kana Arima suggested that he'd look back at his happy memories in Chapter 50 to improve his acting on the spot. It is a case of Post-Traumatic Stress Disorder and doubles as an active reminder to not stray from his original purpose of vengeance. He blames himself for being weak-willed during that moment, even though he was but a child. He was able to make use of these negative emotions, however, to exemplify his acting performance during his scenes in the Tokyo Blade Theatrical.

Aqua is described as someone with emotional distance, he is shocked when he hears from Kana that he is  gloomy  , despite this, he does genuinely care about the people close to him. Aqua is overly protective of Ruby, his younger twin sister, and is mostly described by Taishi Gotanda, his mentor, as someone with a sister complex that's understandable because he's unwilling to let his sister become an idol and suffer the same fate as their mother. Thus, he surreptitiously destroys every chance her sister may get to be promoted due to this overprotective nature, despite knowing how she'd long to be famous. He helped the new B-Komachi group in preparing for a gig so they could accomplish a task long thought impossible. He was also one of the main driving forces behind a project that served to save Akane Kurokawa's reputation.

Etymology

 * The name Aquamarine means "love, affection" (愛) (a), "long time" (久) (ku), "love, affection" (愛) (a) and "sea, ocean" (海) (marin).
 * His nickname Aqua means "water, sea-blue, one from water" in Latin.
 * The name is also associated with a blue-green color, which reflects his eye color.
 * Aquamarine's surname Hoshino means "star" (星) (hoshi) and "field, wilderness" (野) (no).

Trivia

 * Everyone calls him "Aqua" because "Aquamarine" is too long.
 * Ai had one star in each eye whereas Aqua inherited a star in his right eye while his sister Ruby inherited it in her left eye. After the revelation that his "father" was 'dead', he lost the star, implying it is a feature that is dependent upon their emotional state.
 * Possibly due to memories from his past life, Aqua reveals that he can't really use technology as the youngsters do nor does he understand the reason behind their popularity.
 * Aqua is constantly called and labeled a sis-con (a person with an unusually strong attachment to their sister).
 * Aqua spent over five million yen when trying to find out who his biological father is.
 * Aqua dislikes bell peppers.
 * Because Aqua gets acquainted with many female seniors (Kana, Akane, Mem-Cho...), Ruby thinks his type is older women.
 * Aqua is shocked by Kana's comment that he looks gloomy, this wasn't something noticeable to him himself, although it is a common perception of him.