From the summary on Archive of Our Own:
Shiro has been living with the Avengers since his rescue from Hydra two years ago. However, a young teen genius visits during one of MIT's annual expos and shakes up his world. Now Shiro must contend with the fact that Hiro claims he's his brother on top of his duties as an Avenger, a college student, and Hydra's latest attempt to take him back. Maybe he should have rethought the idea of being a superhero.
Rising Sun
is a Fan Fic written by Charbonne, a crossover between the Marvel Cinematic Universe and Big Hero 6. The story revolves around Shiro, a young man found in Hydra custody who is suffering from a severe case of amnesia and somehow developed fire powers, being discovered by the Avengers and ultimately becoming a part of the team. However, Big Hero 6 discovers Shiro and his uncanny resemblance to Tadashi, Hiro's long-thought dead brother.
Rising Sun provides examples of:
- Amnesiac Hero: Shiro can't actually remember who he used to be and actually believes he's a clone of Tadashi.
- Broken Pedestal: Callaghan to Shiro/Tadashi
- Call-Back: Hiro's appraisal of Baymax 2.0 is reminiscent of a similar scene in Big Hero 6.
- Defiant Captive: Shiro is this to Hydra.
- Enemy Within: What the Avengers were afraid that Shiro might be.
- Gadgeteer Genius: Shiro is able to impress Tony Stark with his knowledge of robotics and programming, and even rebuilds Baymax, though improves him with fire-retardant material. Naturally, he made improvements to the robot based on what Hiro suggested before. Hiro and Tony are also examples of this.
- Genius Ditz: Fred shows signs of this as well as Genre Savvy.
- Human Shield: Callaghan tried to stop Hydra from kidnapping Shiro, only for Hydra to pull this.
- Identity Amnesia: Shiro has no knowledge of his past as Tadashi Hamada, though he does have brief instances of things being familiar to him.
- Kidnapped Scientist: Fred believes that Shiro is a victim of this.
- Nebulous Evil Organization: Hydra.
- Superhuman Trafficking: Why Hydra kidnapped Shiro.
- Traumatic Superpower Awakening: Tadashi's abilities surfaced as a result of being in the fire that killed him in Big Hero 6.
- Vehicular Kidnapping: Shiro has a dream where this happens to him.
- You Are Grounded!: Cass pulls this as she's praying to her brother and sister-in-law when she addresses Tadashi by stating that he's grounded until he's thirty "at least."
