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 known as Gorou in his past life, a medical doctor who treated patients. He developed an obsession for idols (specifically for Ai Hoshino, an idol of the defunct idol group, B-Komachi) after encountering Sarina, one of his patients who held 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 Hoshino.

In his new life, after the death of his mother, he swore he'd do anything to find whoever was behind her murder; unrelenting in his goal despite numerous years passing, unlike his sister. Many of his actions are driven by this very ambition. He is willing to do anything to get closer to the truth including committing murder.

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 one halves of their mother. When he was a child, he was often called cute by those around him.

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

Personality
Before the death of Ai Hoshino, Aqua was considered relatively normal other than his unparalleled prodigious talent in acting. However, with him retaining the experiences of his past life, he was able to accomplish many things not expected for someone of his age. Performing acting jobs was something he was open to and excelled at.

After his mother's death, however, he was a changed person. He became cold, calculated, cunning, and discreet. He transformed into a man willing to do anything to see his goals through.

Despite this, he does genuinely care about the people close to him. He's unwilling to let his sister become an idol suffer the same fate as their mom. 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.

After being told that his father, the main reason for his quest for vengeance was dead, he becomes more warm to those around him and began smiling more. He ponders whether he could now be happy and live normally as he recalls his girlfriend's smiling face. Moreover, he becomes more supportive of Ruby's ambitions and encouraged her to do her best. He was deeply ashamed of himself for continuously using Akane for his own selfish ambitions, but after she broke down, he wiped her tears and vows to keep her safe as he gave her their second kiss that was removed from ulterior motives.

Prologue
Gorou was a 30 year old doctor and a huge fan of the idol Ai. He was his fan because of a 12 year old patient of his named Sarina used to adore her, before she eventually died. When Ai was pregnant, she came to Gorou's hospital to give birth to twins. Because he was in charge of her, he was murdered by an anonymous stalker and was reincarnated into Hoshino Aquamarine, the son of Ai.

At the age of 4, Aqua witnesses his mother getting stabbed by that same stalker after answering the door, who later committed suicide. However, Aquamarine thinks it's more than a simple "crazed stalker" situation and believes the stalker had been given information about her location by someone close to Ai, which he theorizes is their unknown father and swears to avenge his mother's death by killing him. Even in the future, this single event traumatized and transformed him into who he is today, so much so that he is seen preventing his sister from becoming an idol, afraid that the same events may reoccur. Although he did get a change of heart after Miyako Saitou, his parental figure, conversed with him about it.

Entertainment World
Not long after, Aqua and Ruby applied to Yoto Highschool, a school that offers The Performing Arts Program, the program Ruby enlisted in. Coincidentally, Kana Arima, an acquaintance of the two siblings, was also a part of the school. Aqua reveals his intentions of joining the school was being worried about his sister, Ruby then labeling him a sis-con after the fact.

After Kana made attempts to catch up with Aqua, he allowed her to meet with Taishi Gotanda, allowing them to talk in a more private area. Their conversation eventually led to Aqua's interest piquing after Kana mentioned an affiliate of Ai Hoshino, Kaburagi Masaya. Since he was involved with a project Kana was in, the live-action Sweet Today drama, Aqua uses this as an opportunity to gain more intel about her murder, suspecting Kaburagi to be a potential candidate as his father. The drama was generally received terribly due to incompetent actors and a butchered storyline. Kaburagi's attention was raised when Aqua and Kana acted out a genuinely good scene in the series finale. This provided leeway for Aqua to talk business with him, Kaburagi stating he'd provide info about Ai's background if Aqua acted in a reality dating show.

Dating Reality Show
In the show, he perfectly played his character, went with the flow of the show with his other colleagues. Later on, he was one of the key coordinators behind a project to save Akane Kurokawa's reputation in the public's eyes (due to a moment involving her and Yuki Sumi.) He was also able to save Akane from jumping off the bridge in the nick of time, reassuring her that it's alright. He was exasperated at how toxic the fans was and how the adults exploited her for their own profit. On his part, he went out of his way to threaten those very adults and pulled multiple all-nighters to make the perfect video to change the minds of the fans.

After introspecting her situation, she decides to have a new outlook not too dissimilar to Ai Hoshino for her and the show's sake. This surprises Aqua, and made him blush when he first saw how similar they both were. However, upon conversing with Kana, he realised that he was still trapped from his feelings for Ai and not the current Akane. Aqua reflects upon his relationship with his mother, showing him how much he never really knew her. When conversing with Akane and realizing how in tune she was to her character, he started seeing her as someone indispensable for his goal. For their last episode, he went above and beyond as he gave both of their first kiss live, much to Akane's joy.

Upon the show's end, Kaburagi congratulates Aqua for the positive reviews garnered in LoveNow, the reality dating show, received due to his presence. Kaburagi then stated he'd fulfil his end of their bargain in the coming week. After their conversation, Akane approached Aqua regarding their relationship (whether it was the real deal or for business. Aqua confirming that for now, it was the latter). Though to appease their fanbase, subsequently they went on many dates together. Later after the casts get together, Aqua chatted with Mem-Cho. She reveals that she always aspired to be an idol, but didn't due to her circumstances. Aqua then suggested she join the revived B-Komachi that was in the works.

The First Concert
After the new B-Komachi was established, Aqua then headed to discuss with Kaburagi Masaya, about Ai. During their discussion, "The Lalalie Theatrical Company" came into the conversation - the place Akane Kurokawa worked in and where Ai first fell in love. Kaburagi stated that he could get in touch with their head, mainly profit off of it. Later on, Aqua involved himself with the newly established group, helping them to prepare for their new gig by disguising as Pieyon, an internet personality.

2.5D Stage Play
Kaburagi Masaya, after being told about the stage play of the manga, Tokyo Blade, suggested for Aqua and Kana to join the stage play. The representative of the company behind the play, Raida Sumiaki agreed, seeing it as him doing a favor. All went swimmingly until the mangaka behind Tokyo Blade, Samejima Abiko, visited the practice for the play, along with Kichijouji Yoriko (the mangaka behind Sweet Today.) Abiko stated that what she saw butchered the image of her manga and wanted a whole rewrite of the play. Later on, Aqua, along with his fellow actors, visited Yoriko and talked to her about the industry, leading them to convince her to talk to Abiko.

After the script was rewritten and the misunderstandings were cleared up, things went by as usual until Kana indirectly reminded Aqua about his past when she advised him to recall something that makes him sad if he wants to be realistic. This causes him to have a panic attack and collapse on the floor. As his girlfriend, the director then tells Akane to take care of Aqua. Once alone, Aqua tells her not to inform his family of the incident as he didn’t want to worry instead and instead call somebody else. Taishi arrived at the scene and started conversing with Akane about his past. Taishi then entrusts her tidbits of his past due to her girlfriend status which Akane was then capable of piecing the puzzles together perfectly.

Unbeknownst to Akane before, her theory that Aqua was Ai's son was actually true. When Aqua woke up, he was surprised to see Akane crying on his bedside. When asked for the reason, she immediately hugged him and empathize with him that if her thought was true, it would be terrifying as he'd had no one to confide in and it would be incredibly tragic. Aqua remained speechless as she reassures him that no matter what happens, she'll always be by his side and that she'll share his pain if there's something hurting him. The awe-stuck Aqua asks what she was talking about with her reply being that it was a scary thought she had.

After they went home, Akane made a feast for him which surprises the others of her excellent cooking abilities. Initially, he tried to play off that he has no appetite which caused Akane to hand feed him. Slightly embarrassed, he began eating while commenting that it was delicious in his mind. Afterward, Akane asked if she could see the films when Aqua was younger. Taishi was surprised when Aqua gave his permission despite previously adamantly hiding it though he told them to watch it without him. At night, Akane went to visit Aqua on the balcony. She then asked for the reason he was in theatre, be it for fame, fortune or something else. Aqua attempts to dodge the questions though Akane remain steadfast in her pursuit. Finally relenting, he reveals the truth that he’s in it to kill someone but because he is high up, he needs power. He then redirects his gaze to her and inquires what she will do about it.

Without hesitation, she answers that she'll help kill them which caught him off-guard and told her not to say it so casually. She reaffirms her statement that for someone like him, he would have a good reason for doing something so drastic and it’s not a matter of right or wrong for her. Rather, she is willing to accept the guilt along with him as that was how committed she was to their relationship. Though she would also like for him to do his part as her boyfriend, which was to help defeat Kana and Himekawa as she stood no chance alone and would probably die from being too upset at losing. This causes Aqua to reflect deeply as he promised her that he'll to do his part as "boyfriends are responsible for keeping their girlfriends from dying".

Both of them then went to consult Taishi for advice and if possible to do it without emotional acting. After reviewing the script, the only conclusion was simple, with Aqua saying that it'll be extremely passionate emotional acting. Taishi smiled as he says that starting tomorrow, he'll drill it into him from scratch.

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 on 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 Hoshino (Aqua's mother) had one star in each eye where Aqua inherited a star in his right eye while his sister Ruby Hoshino inherited it in her left eye. After the revelation that his father was 'dead', he lost the star, implying it’s a feature that is dependent upon their emotional state. The only other person which had stars in both eyes was Akane Kurokawa when she was acting as Ai.
 * Aqua reveals that he can't really use technology like the youngsters do nor does he understand the reason behind their popularity.
 * Aqua is constantly called and labelled a sis-con (a person with an unusually strong and probably sexual attachment to their sister).
 * Aqua spent over five million yen when trying to find out who his biological father is.
 * Aqua dislikes bell peppers.