my memory is terrible so bear with me:

this was only a small part of the anime, but there was this portal in the middle of nowhere that was reopening, and it was allowing undead demons back into the world. theres also this powerful demon trying to escape too -- hes kinda like the king of the underworld or something. regardless his name holds CRAZY weight.

the main character has to go into the portal (i think to try closing it), but its a race against time because staying in that world for too long is a death sentence. like not only is it just dangerous but being in there basically drains your life essence.

then they end up being captured by the "queen" of that world, OR they find her temple to talk to her/negotiate about the open portal or something.

it definitely has fight scenes throughout the entirety of the anime -- and like right before they enter the portal, or right after they leave, there is a big fight scene.

ALSO i think there was someone else that had to stand outside the portal while the other person(s) went in to make sure the portal stayed open, and to fend off any entities that tried escaping.

PLEASE HELP IM GOING CRAZY

EDIT - more details :

i think one of the main characters is a guy! and i feel like the surrounding area of the portal is a barren desert -- but i could be wrong. and the fight scene i talked about, i think there were *at least* two enemies.

also for the powerful demon, i swear theres a scene where he is chilling on top of a bunch of dead bodies like its his throne. regardless the entire area he hangs around is red. i think he also tries possessing another body because his original form is too weak to carry him outside of the portal.

this could be the entire anime, and im just thinking it was a small portion of it!!