As the two are from different DreamWorks series, they have never met in canon.
Both Astrid and Toothiana (more commonly known as Tooth in the RotG film) are the main female characters who are very close with the main protagonists of their DreamWorks films, Hiccup and Jack. Because Tooth is a fairy she can fly through the air at will, while Astrid needs the help of her dragon and friend Stormfly, along with Astrid using her dragon scaled flight-suite to glide in the air. Before and after Astrid became a dragon rider, she helps her friends protect Berk and wild dragons as their defenders, while Tooth is a Guardian of Childhood and one of the first four members as the Guardian of Memories when she isn't serving as the queen of teeth collecting fairies, that help her keep the childhood memories within the teeth safe. When Astrid was little she lost her uncle, while Toothiana lost her parents in the original Guardians of Childhood books.
Tooth is the mother and queen of her bird-like tooth fairies, that she created to help her collect teeth from around the world, while Astrid's dragon has a bird-like poster and had been an aunt to Stormfly's babies before both dragon and rider became very close with the Death Song dragon they saved as an egg and later raised Graff for a bit until placing the dragon in the care of an adult Death Song that can properly raise the young dragon in the wild. Their bond with Graff become strong after they re-met him as a teenager dragon who got injured when his adaptive parent got captured by Dragon Hunters.
Astriana is a secondary/honorary femslash ship of the Rise of the Brave Tangled Dragons crossover, where Hiccup and Jack are part of the Big 4 along with Rapunzel from Tangled and Merida from Brave, that sometimes has Astrid and Toothiana as two of its secondary or honorary members of the RotBTD crossover. They are also largely/mediumly part of the three other DreamWorks crossover fandoms, How to Train Your Guardian, The Big Four Ladies (where they take Hiccup and Jack's places in the Big 4 fandom) and the DreamWorks Ladies (with Eep Crood from The Croods and Tip Tucci from DreamWorks' Home beside them). It is less popular than Hijack, then though in its own way it is a femslash version of the HTTYD/RotG slash ship. Since fans commonly feature the two female characters in Hijack fanfics, along with both of their rival het ships Hiccstrid and Frostbite.
In many fanfics, Toothiana is commonly portrayed as the feminine one, since Astrid is more likely to be the dominant one of the two DreamWorks characters. Along with many fanart of the ship commonly having Toothiana in her human form, which is usually of South Asian origin, due to her origin being set in South Asia. The common shared fan idea is mostly seen in modern AUs. Some even have Astrid believing in Tooth as a child and later meets her as a teenager, once her belief in the Tooth Fairy is restored.
On AO3, the ship has 10 fanfics on it. As well as the ship having small fanbases on both DeviantArt and Tumblr.
|SHIPS||het||Astret • Dagala • Heatcup • Heathlegs • Hiccelsa • Hicclena • Hiccstrid • Mericcup • Moaccup • NightLight • Stalka|
|femslash||Astriana • Valkinor • Valkstrid|
|slash||Dagcup • Eretcup • Hijack • Variccup • Ketchup|
|family||Stoccup • Valccup|
|friend||Dagurmaster • Toothcup|
|CHARACTERS||m/f||Hiccup Horrendous Haddock III|