A young and idealistic diplomat from Earth could be a main character. They initially try to avoid war but are pushed aside by the warmongers. As the war rages, they try to find a way to end it. From Asgard, Heimdall could be a main character. With his all - seeing abilities, he is constantly watching the Earth's moves and reporting back to Asgard, playing a crucial role in their defense strategy.
On the Earth side, it could be a military general who is leading the charge against Asgard. He might be a tough and battle - hardened character. On the Asgard side, Thor could be a main character, as he is one of the most well - known Asgardians. He would be trying to protect his home and people from the Earth's attacks.
Maybe a scientist on Earth who discovers something about Asgard that sets off the war could be a main character. They might be a bit of an anti - hero, thinking they are doing the right thing for Earth but actually causing chaos. For Asgard, Loki could also be a main character. He might be playing his own games during the war, either helping or hindering Asgard depending on his own motives.