Heimdall is the Guardian of the Rainbow Bridge. After Odin sculpted humanity, there is a story in heathen Lore that the god Rig then fathered new kinds of humans, and most Asatruars consider Rig to be a name of Heimdall. 

In the Fireverse, Heimdall is partly a participant in a lot of the shenanigans that Thor and Loki get up to in Jotunheim, because he is the one who lets them in and out. He opens the Bridge for them when they go and listens for them to call on him to send down the Bridge for their return. He’s a friend to both of them. There is Lore that Thor does not walk on the Bridge because his mighty footfalls would destroy it, but in the Fireverse he walk on it like everyone else.

At Ragnarok, Heimdall and Loki both know the Prophecy says they are supposed to fight to the death, but in the Fireverse it doesn’t go that way. They meet on the battlefield, thinking it’s time to do one last job before the end, and something completely different happens.

The Fireverse is written from the perspective of Loki so the way the story of the theft and return of Freya's jewel is depicted in the Fireverse is slightly different than the way I told the story of Heimdall's Initiation on my video for the Rainbow Season ritual, which was told following Heimdall's story instead of Loki's as the primary story. View the video Heimdall's Initiation here: https://www.youtube.com/watch?v=hlitP7Zyv1I&t=213s

Image: an altar piece honoring Heimdall that I embroidered. It includes a rainbow, a horn, a sword, runes, and Heimdall's three sacred animals: the ram, the seal, and the woodpecker.