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In Black Lion, Nobunaga is actually possessed by alien invaders who equip his armies with high-tech armaments so he can conquer Japan as a beachhead (probably; the backstory isn't covered much).
In Drifters Nobunaga is a human warlord, but revels in his reputation and has no issue presenting himself as a demon. He's more of a Magnificent Bastard.
In Samurai Deeper Kyo, Nobunaga was Japan's fiercest warlord who has a massive hate on for the main character. True to his nickname, his powers all revolve around Grim Reaper based attacks.
In Wrath of the Ninja, Nobunaga appears to be the chief antagonist for the 3 heroes, conquering Japan with demonic help and seeking to be transformed into a demon himself. This time, however, there's a Man Behind the Man, a demon looking to use the bloodshed of war and Nobunaga's cruelty to power the demons themselves, and Nobunaga is just his patsy.
In Blood Reign Curse Of The Yoma, Nobunaga doesn't directly appear, but the story takes place at the height of his conquests, and he influences the story since the main character is a ninja serving the Takeda clan when it opposes Nobunaga, and because the brutality of Nobunaga's conquests is giving power to the Yoma demons. At one point the main character thinks about Nobunaga's brutality and wonders if he is a demon. While he's doing this, Nobunaga and his army are seen in a montage, and all of them have glowingred eyes.
In Kamen Rider OOO's movie, the Kougami Foundation created a Homunculus copy of Nobunaga; since he was made from the same materials as the villainous Greeed, he ends up becoming a similar creature. However, this is revealed to be involuntary, instead acting as a Super-Powered Evil Side who comes forth to seek revenge on the descendants of those who killed the original Nobunaga.
The Call of Cthulhu supplement Secrets of Japan reveals that Nobunaga is but one of Nyarlathotep's thousand masks, and that the Outer God still occasionally pulls him out for, of all things, business meetings.
In Persona 2 there are monsters/Persona based on Nobunaga called "Demon King", in Japanese, it's called "Dairoku Tenmaoh". Later, in Persona 4, Kanji Tatsumi's evolved Persona is a shortened version of these demon/Persona: "Rokuten Maoh".
And the third game (and The Movie of the anime) does even better when Nobunaga returns Like a Badass out of Hell, having apparently taken over the sixth underworld and turned his epithet into a literal description. As a playable character, his story pretty much involves killing everyone else in Japan before returning to hell.
Samurai Warriors doesn't have Nobunaga as a bad guy specifically (unless you're playing the first one or as an enemy of his on any of them. Then, like the rest of the three rulers, he's a ruthless SOB as always. And even being an ally doesn't always mean he's not portrayed as unnecessarily cruel.), but it doesn't stop him from wielding dark magic and being able to charge his sword to sound like a freaking lightsaber!