Shounen ga Otona ni Natta Natsu

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Shounen ga Otona ni Natta Natsu (Boy grow up in summer) is an 2023 Hentai manga by Jairou, first released in between 2022 and 2023 on adult magazine Comic MILF.

Kirishima Ryuuki is a young football prodigy living on his own since his parent died and her beloved older sister Reiko, a chemical genius who practically raised him, moved to Tokyo for work. Ryuuki has never shown interest in any girl (except perhaps his sister), until his friends introduce him to a new porn actress, Kirill-sama, by whom he is immediately smitten. What a coincidence then that Kirill happens to pass around those parts when the boy is busy watching one of her videos...

A 4-episode animated adaptation produced by Queen Bee started releasing in September 2024.

Tropes used in Shounen ga Otona ni Natta Natsu include:

• A-Cup Angst: Invoked by the secret password of the boys' club:

Friend: What's the password?

Ryuuki: Huh? Just open the door already. Friend: No exception, spill it quickly. Ryuuki: Bruh... Forgive me, Ueno-chan.

Ryuuki: The malicious Chiaki with the small bosom.

• And the Adventure Continues...: The story ends with Ryuuki and Reiko deciding to continue their secret relationship, while still using the latter's Kirill identity to involve Ryuuki's friends and Chiaki to make "new thrilling memories".
• Becoming the Mask: Proper and studious Reiko created the carefree and lascivious Kirill persona to have an outlet for her sexual desire and her repressed love for her own brother. The plan backfired, as her desires did not abated but rather she ended up using the fabricated persona to realize her incestuos fantasy, losing control of herself.
• The Bet: Kirill challenge Chiaki to one for Ryuuki's love: let herself be recorded going streaking around school without getting caught and Kirill leaves forever, fail and Chiaki will have to debut in an adult video with Kirill. She accepts.
• Brother-Sister Incest: Ryuuki has clearly a thing for his older sister Reiko, to his embarrassment.
  • But as it turns out, Reiko has an even bigger thing for him, as she becomes willing to create an entire new identity just to have a single chance to hook up with him.
• Caught with Your Pants Down: Kirill meets Ryuuki in the forest right as he's masturbating to one of her videos.
  • Chiaki is caught peeping from a bush on Ryuuki and Kirill with her panties down.
• Chekhov's Gun: Ryuuki's precious game card that he gifts to Kirill after their first time.
• Childhood Friend Romance: Chiaki has a crush on Ryuuki, which Reiko notices and approves of.
• Coming of Age Story: As the title suggest, this is the story of how Ryuuki became "a man".
• Cool Big Sis: Reiko is this to Ryuuki, who is fiercely defensive of her and her accomplishments.
• Genius Slob: Reiko is a chemical genius, but she is also unkempt, plain and portly.
• Love Triangle: Both adult streamer Kirill and childhood friend Chiaki are in love with Ryuuki.
• Making Love in All the Wrong Places: Kirill loves exhibitionism, and Ryuuki soon learns to appreciate it too.
  • The last chapter see them having outdoor sex around town during a storm alert.
• Porn Names: As expected for AV streamers, Kirill is not the woman's real name.
• Promotion to Parent: Ryuuki and Reiko's parent died in an accident when the former was but a baby, leaving the latter to raise him. Ryuuki admit to himself that he consider Reiko his real mother, rather than the one he can't even remember the face of.
• Secret Identity Identity: Kirill is acutally Reiko, Ryuuki's older sister. In a uncommon inversion of the usual trope, it's actually the public Reiko identity the one requiring more work, as Reiko uses form-suppressing bra, a fake belly and a jaw prosthesis to differentiate herself from her usually naked fabricated identity, for which she only need hair dye.
• Shotacon: Kirill has no problem having sex with young boys or dating one of them.
• Skinny Dipping: In the second chapter, Ryuuki and his friends do this due to an unplanned swim in the river.
• Team Mom: Chiaki Ueno has this dynamic with Ryuuki and his friends: they find her bossy, but Ryuuki see her kinda as a second big sister.
• Teen Genius: A realistic but still impressive example: Reiko Kirishima managed to become one of Japan's top chemists before her mid-20s, all while raising a younger brother on her own (which mean she had to forego, among other things, going oversea to study or work).
• Whole-Plot Reference: The story premise is a pornographic version of The Strange Case of Doctor Jekyll and Mr. Hyde, which is referenced by Reiko herself. Surprisingly, it actually sticks closer to the original work than many other works relying on the Jekyll and Hyde trope: Hyde/Kirill is not a completely different person from the original Jekyll/Reiko, just a useful mask created by the latter through scientific means to allow them to live their urges without social repercussions.