Their babies could have a combination of Toothless's black scales and Stormfly's greenish - blue scales. Maybe they would have Stormfly's long, slender body shape with Toothless's large wings. They might also inherit Toothless's bright blue eyes.
The babies could have a color pattern that is a blend of Toothless and Stormfly. For instance, they might have a black base color with greenish - blue markings all over their bodies. Their horns could be small at first, but as they grow, they might develop into a shape that is a combination of the curved horns of Toothless and the straighter horns of Stormfly. Also, their claws could be sharp like both parents, but with a unique shape that is distinct to them.
Toothless is known for being intelligent and curious. His babies might inherit this, always getting into little adventures to explore new things. Stormfly is feisty and strong - her babies could be brave and not afraid to stand up for themselves. So in a fanfiction, the Toothless babies might be the ones coming up with the ideas for exploration, while the Stormfly babies are the ones ready to fight any danger that comes their way.
The fanfiction might explore the reactions of the other dragons in their community. Some dragons could be jealous, while others might be helpful. It could also focus on the growth of the baby dragons. They might start off small and cute, but as they grow, they develop their own personalities. They could be mischievous or very serious, just like real - life children.
One possible plot could be that the babies get lost during a big adventure. They end up in an unknown part of their world and have to learn to work together to find their way back home. Along the way, they meet new creatures and have to overcome various challenges, like crossing a big river or getting past a group of unfriendly animals.
Hiccup would probably be overjoyed. He has such a deep bond with Toothless, and seeing Toothless become a father would be a very special moment for him. He would likely be very involved in helping Toothless raise the babies, teaching them things he has learned from his own experiences with Toothless.
Hiccup, Toothless's rider, would probably be quite surprised at first. But then he'd be happy for Toothless. He knows how important relationships are, and he'd see it as a sign of Toothless growing and experiencing new things. Astrid, Stormfly's rider, might be a bit more protective at first. But once she sees how much Stormfly cares for Toothless, she'd come around and support them.
One possible plotline could be the growth and development of the baby dragons. Maybe they inherit unique abilities from Toothless and have to learn how to control them. For example, if Toothless has a special fire - breathing ability, the babies might start to show signs of an even more powerful version of it and they need to be trained to use it properly.
Maybe the baby dragons get lost outside the Hidden World. They encounter different challenges like facing hunters and strange new landscapes. Toothless and Light Fury are desperate to find them. Along the way, the babies make new friends among the local animals who help them survive. The fanfiction could detail their adventures and how they finally reunite with their parents.
An ancient and evil force that was once sealed away but has been awakened by the birth of the baby dragons. This force is drawn to the pure and powerful energy of the babies and wants to corrupt them. It uses dark magic to try and influence the babies' minds, and Toothless and Light Fury have to fight this powerful and mysterious foe to protect their young.
Bolt would likely become more protective. He is already a brave character, but with the impending arrival of babies, he'd be on high alert all the time. Mittens, on the other hand, might become more nurturing. She'd start showing her softer side more often.
They would probably raise them with a lot of love and protection. Given their own experiences, they would want to shield their babies from the dangers of the supernatural world as much as possible. At the same time, they would also teach them how to use their powers responsibly.