Night Fury (Loki x Fem!Hiccup x Bucky - Soul...
When Loki and Thor were mere teens (A few hundred years old) they were introduced to the dragon riders of Berk, among whom Loki found his first soul mate, Hedvika Horrendous Haddock, or Hiccup. Unfortunately years later she was 'killed' in battle when she fell from her dragon, Toothless who was unable to save her. (In reality, she survived the fall but the joining of Loki and Hiccup was deemed unwise for the Nine Realms by Odin and Stoic (Hiccup's father) Was forced to exile her and Toothless from their home)
Many hundreds of years later after failing to invade Midgard (Earth) Loki is sent back to Earth to do penance for his crimes, there he meets his second soul mate, Bucky Barnes, the Winter Solider. Both repenting, both broken and a little dark inside. But something is missing. Loki knows it to be Hiccup but he keeps it from Bucky.
What happens when they get reports of a dragon too fast to see clearly? And a rider sat atop it's back?
Book Six of the Avenger soulmate books - Bucky Barnes and Loki Laufeyson (Birthmark)