Nioh and Nioh 2 (including all DLCs) are also bundled in the Nioh Collection on PS5.
The Twilight Mission Evil in the Ether requires that you have unlocked the Main Mission A Defiled Holy Mountain to access it.
Twilight Mission – Evil in the Ether Walkthrough
The Twilight Mission begins with William at the entrance of a cave in Mt. Ibuki. Equip a Suppa Scroll if you have one, as it reduces the chances of an enemy noticing you. However, remember that it also reduces your defense once used, so be careful when moving past opponents.
Enter the cave, taking the left-hand path going inside. The first space you will encounter will have two Bloody Graves standing inside; you can challenge the revenants that will appear, or keep on moving. Continue on the path until you arrive at a bigger room with several more Bloody Graves and patches of grass.
Climb the slope at the northern end of the room and try to dodge the arrows from the archer standing near the first turn. Take it out, then head along the path. Make a second turn, then turn left at the passageway with a brazier standing near the entrance.
The passageway will end at a ladder. Press O to descend, or jump down to the lower level. There is a Bloody Grave and a Flying Bolt, or Ittan-momen waiting in the area. Take out the wraith, then continue on the path until you reach an elevated area lit by two braziers. Go up, but be careful of a One-eyed Oni that will spawn here. Either defeat or evade the Oni, then enter the area beyond.
Take the right-hand path at the junction, keeping an eye on the left wall where you will see a ladder. Don’t jump down, as the fall will deal damage to your health. Press Circle to climb down instead. You will end up at a shrine. Make some offerings if you need to power up your equipment and enhance your abilities, then climb back up the ladder.
Once you’re back on the upper level, retrace your steps back to the spot where the Oni appeared, then find the narrow bridge in the area. It is pretty hard to spot, but keep on mind that it has a Bloody Grave located just before it.
Walk along the bridge. There is a trap sitting in the middle of the bridge, meaning there is no way to evade damage. Take the hit to your HP, staying on the path. Cross over to the other side and enter into the passageway. You will end up at a path with grass and Bloody Graves. Walk along the path, following it as it curves to the right and climbs up. At the end of the path is a brazier standing in front of a door.
Enter the door and go through to the other side. Drop down to the narrow ledge along the side of the door to find a Shrine. Loop back, and continue down the stairs leading to the door. There is a Bloody Grave at the foot of the stairs as well as a hanging bridge. The revenant in the Bloody Grave may attack you as you are trying to cross the bridge.
As if you don’t have anything else to worry about, a One-Eyed Oni will appear and block your path. You can run from him though. Watch out for fire traps once you’ve crossed over to the other side. There are also Bloody Graves, Yoki and Wheelmonks lying in wait further up the path. You will end up in a wide space with a tall staircase. The room at the foot of the staircase has a shrine inside.
Boss: Ishida Mitsunari
Main article: Ishida Mitsunari
Climb the tall staircase until you reach the building at the top. There is a Bloody Grave inside that will spawn a revenant. Continue out the second door, then through the third one. You will end up at a large room with the boss of the Evil in the Ether Twilight Mission: Ishida Mitsunari.
Mitsunari will use his air slash ability to deliver long-range damage. Start by climbing the slope on the right side of the room, baiting him to follow you. Once he’s close enough, drop down the side of the slope and loop back to his location. Stick to low stance to maximize your movement speed and keep hitting his back, repeating the process if you end up facing him.
Was this walkthrough for the original level 145, or a NG+ level? Because level 145 doesn’t feature most of what you mentioned.