Forest Oni

The Forest Oni is the boss creature of Tokyo Breach.

Heroes
As with all Boss Monsters, Heroes need to coordinate and work together to survive and overcome the battles with these creatures. The Oni in particular is a high damage dealing Warrior with multiple hard-hitting attacks that affect an area. However, it would be a disservice to not mention that as of 1/24/2019, the Oni is considered one of the easiest Boss Fights in the game. Almost every single one of his abilities has an easy to dodge wind up that makes a lot of the potential damage the Oni has vanish into thin air. It can get to the point where the only time the Oni does any considerable damage is where he builds up a Shockwave, since the only way to escape that is dodging out at the last second or becoming Immune to damage. Against AI, you should almost always win the fight, even if you're behind on Objectives. Against player VDs however, things get more complicated. Since the VD can choose to place things such as cages or walls, they can purposely wall off your Support Heroes and, if skilled enough, take them out of the equation. While that may sound problematic, it's recommended to still wail on the Oni, since it's got very few tricks up its sleeve aside from that. It is highly recommended to bring ranged dps for the fight, since all of the Onis attacks are melee range aside from his Gut Pull, and you can just dodge out of that before the Oni pulls off any other moves. The main strategy for fighting it is keeping a Tank in its face at all times, while dps whittle it down and the support try to stay out of danger. It'll occasionally summon "Onigiri Orbs" during the fight, and its recommended to take care of them to make the fight easier, but in the current build of the game you can ignore them and take the Oni out anyways. If you're the Tank for your team, then just remember that while you should stay in its face constantly, that doesn't mean that you should take every hit he dishes out. Purposely choosing to take the Oni's high damage at face value is a recipe for disaster, and is one of the few situations that leads to an Oni win. Be smart, give the Oni plenty of room, and the fight should be a cakewalk.

Veil Demon
As a Veil Demon (VD), playing Oni can be complicated, and a lot of the time your main focus might not even be playing as the Oni, but as an Elite. Since you can always tell before a match starts what kind of Boss you'll have to work with, you can pick complimentary Elites to help resolve any issues that may arise. For the Oni fight it is highly recommend that you pick the Komainu Annihilator for its pin and overall damage, and a Feral Buta for, once again, for its pin and overall damage. Manhunter can be a good decision as well if you really can't stand the Feral Buta, but the Pin is really handy for locking an enemy down for the Oni to hit. Playing as the Oni right off the bat is not recommended; if you are adamant about possessing it, make sure to place plenty of traps around the arena that you plan to abuse FIRST, then go ahead and possess the Oni. Since a lot of your abilities are incredibly easy to dodge or even just walk out of, it'll be essential to have those traps tripping up the rest of the enemy team. As mentioned before, you want pin Elites purely for the fact that you can pin down either a support and prevent the enemy from supporting whoever is tanking the Oni, or even just pinning the Tank itself and forcing them to take the brunt of the Oni's attacks. If you get to the point where Onibi Orbs start appearing, you've reached a gray area of the fight. See, by this point, you've probably already reached half health and are working out ways to fight off the Heroes. Alternatively, you'll be getting a damage buff from this point on, and any enemies you manage to hit while pinned are probably getting downed in a few hits. And honestly, that's about all there is that you can do for the Oni fight in its current state. Gut Pull is good for snagging ranged dps or supports, and the rest of your abilities are essentially useless unless the enemy is new, lagging, or pinned by one of your elites. Your best chance is to have denied as many of the objectives on the way up to the boss fight as possible, even if you're wasting abilities to do so, just to ensure the enemy Heroes are as weak as they can possibly be when you have to fight them.

Additional notes

 * The Forest Oni is based on the Oni from Japanese folklore.