Chapter 1

7-year-old Tsunami was abandoned and left to die by her parents who favoured her twin sister more. Tsuna, believing she deserves to die, just sits there accepting her fate when Natasha and Clint come across her. Natasha decides to adopts her once she hears of her past.
After Clint was taken by Loki, Tsuna snuck on board wanting to help free her uncle. After the invasion, she lives in the Avengers Tower until her biological parents want her back for their own nefarious purposes and they have the Vongola backing them up.
(G27(later on though))