Allothogs are large beasts that are used as mounts for the foul Oni. The Oni have been using them as war mounts ever since they've taken and destroyed the planet they once thrived on. The Oni like to use Allothogs rather then horses or other mount like breeds on their planet cause they can be trained to be really aggressive and violent in battle with the Shinigami, also they're much faster the a horse. Usually Allothogs are not aggressive and rarely attack, but the Oni force them to be vicious, even if it means abusing them. Pitying for the poor beasts, the Shinigami try to rescue the Allothogs any chance they get, when they kill a Oni mounted on a Allothog they'll take it back to their world and re-train and rehabilitate the animal. Luckily they're pretty docile creatures and are easy to tame. Once they're tamed and fully healed from any wounds the Oni might have caused they are released into the wilderness, where they can live out normal, peaceful lives.

Here is a Shinigami saying hi to a tame Allothog and it's calf.