One idea could be that Toothless somehow gets transported to the DMC universe. Maybe he forms an unlikely bond with Dante. Since Toothless is a powerful and intelligent dragon, he could assist Dante in fighting demons, using his speed and fire - breathing abilities in unique ways.
One idea could be a crossover between DMC and a fantasy series like Lord of the Rings. Dante could find himself in Middle - earth, facing off against orcs and demons alike. His swordsmanship and devil - may - care attitude would make for an interesting dynamic in that world.
A plot could revolve around a new enemy that threatens both the world of How to Train Your Dragon (where Toothless is from) and the Devil May Cry universe. The characters from both universes have to team up. For example, Vergil might be initially skeptical of Toothless but then come to respect his power. Toothless could also interact with the different weapons and magic in the DMC world in an interesting way.
A powerful demon lord from the DMC world would be a great antagonist. This demon lord could see Toothless as a threat or a tool to use for his evil plans. He might try to corrupt Toothless or use his power to gain an edge over the DMC heroes.
One idea could be a crossover with the Bayonetta series. Dante and Bayonetta could team up to fight a common, powerful demon. Their different fighting styles would make for some epic battles and interesting interactions. For example, Dante's flashy swordplay combined with Bayonetta's acrobatic and magical combat.
One plot idea could be Fem Hiccup discovers a new ability in Toothless that no one else knew about. For example, Toothless can communicate with a long - lost species of dragons. Another could be Fem Hiccup gets lost in a strange land and Toothless has to use his instincts to guide her back home. And also, a plot where Fem Hiccup and Toothless encounter a powerful enemy dragon and they have to work together to defeat it using their unique bond.
Another plot idea is that a strange illness starts affecting the dragons in Berk. Toothless is one of the first to show symptoms. Hiccup, being the dragon expert, sets out to find a cure. He and Toothless travel far and wide, facing many challenges along the way. They meet other dragon riders from different lands who may or may not be helpful in their quest for the cure. This journey tests their bond and shows how much they rely on each other.
One plot idea could be them going on an adventure together to discover a new, hidden land filled with strange and magical creatures. They have to rely on each other's unique abilities to survive and explore.
Well, a plot could involve Hiccup and Toothless getting separated. Hiccup then has to go on a journey to find Toothless, facing many challenges along the way, like bad weather and other dangerous creatures. Or perhaps they find a magical object that gives Toothless some new, unexpected powers. Hiccup then has to help Toothless learn to control these powers. Also, they could be transported to a different time period, and have to find their way back while also dealing with the differences in that era.
One plot idea could be Fem Hiccup being the only one who can truly understand Toothless's unique abilities and they go on a journey to discover a hidden dragon world that only Toothless can sense. Another could be Fem Hiccup having to protect Toothless from a group of dragon hunters who are after his special powers.
A story could also be about the baby's discovery of its unique abilities. It might be able to do something that neither Toothless nor Light Fury can. For example, it could communicate with a different species of animals in the forest. This causes a stir among the dragon community and also makes Toothless and Light Fury very proud.