After her battle with the red death Hicca exploring takes her to Japan where she encounters a ninja clan that takes her in. Spending the next six years in training she becomes and powerfully skilled ninja and returns home in Berk's hour of need. Using her new skills she shows them she as tough as any viking.
The story is later continued in HTTYD: The Gathering of Shadows.
This series provides examples of:
- Adaptational Badass: While Hiccup in-canon is pretty badass, Hicca is a ninja!
- Big Sister Mentor: Mayumi to Hicca.
- The Clan: The Shadow Dragon Clan.
- Due to the Dead: Ash makes sure that the symbol of the Dragon Training Academy is a Night Fury (despite being the founder) as a tribute to Hicca, who everyone believed died in the battle against the Red Death.
- Evil Is Petty: Daigo doesn't approve of Hicca - an outsider - being a member of the clan, is shown to be jealous of her popularity. He even sabotages a bow she was going to use on a mission so that she would get killed, or at the very least embarrassed publicly (despite the fact that she was leaving anyway). In the sequel, he outright betrays his clan, sides with an enemy ninja clan and travels all the way to berk to kill her as revenge for beating him fair and square in a duel.
- Feuding Families: The reason why Siver is after Stoick is because their families have been out to kill each other for generations, Siver himself having had a scuffle with Stoick over a decade prior.
- Like a Duck Takes to Water: Due to her Mayumi's encouragement and appealing to her intellect, Hicca is able to become an accomplished kunoichi, a contrast to when she was being trained in viking combat which she had no potential for. In-fact, not only was she able to pick-up on ninjutsu better, but she was able to overpower nearly every skilled viking on Berk when she returned.Hicca was apparently really good at not being noticed. She had had years of practice after all.
- McNinja: Despite not being of Japanese descent, Hicca is taken into the Shadow Dragon clan with open arms, and with a few years of training, becomes a talented Kunoichi.
- Parental Marriage Veto: Inverted, as Ash's parents are pressuring him to find a girl, something he wont do because he is holding a torch for Hicca.
- Rule 63: Hicca and Ash are genderbent versions of Hiccup and Astrid
- There Are No Coincidences: One of the reasons why the Shadow Dragon Clan were so quick to allow Hicca to join them is because Toothless resembles what a "Shadow Dragon" may look like and sees him as a fortuitous omen.