This one seems to be more of Warriors Orochi, but it only involves the Samurai Warriors characters, so I'll just ask this. Why in the bloody hell does Date Masamune act like a fanatical worshipper of Orochi that seems to have lost hope in all humanity? Is he turning into the counterpart of Dong Zhuo, the token guy of Obviously Evil in Dynasty Warriors? Okay, I know he has his reasons behind, but when you act like a total fanatic about it, those reasonings seems to be eligible to be thrown into trash and consider him fallen REAL hard (unlike Keiji, who while being a devil-may-care Blood Knight, does understand and respects Orochi's motivation, being Boisterous Bruiser he is).
There's a vague attempt to justify it in Orochi's flashback campaign in the second game—apparently Masamune got a large dose of evil while Orochi was busy crushing the Tokugawa clan and the sight of the abyss broke Masamune into tiny little pieces.
There's a part in Shu's storyline that seems to follow that. After the battle where Ieyasu fails to convince Masamune, Taigong Wang says something on the line that he hasn't been able to get rid of "Orochi's poison". As far as I see it, he has gone so deep in darkness that only someone with a really strong bond would be able to return him to his normal self. That would mean Katakura Kojuro (my wish), his wife Megohime (more wishing for the impossible) and Magoichi (a bit of a stretch, but the only canon solution I can think of)
Doesn't seem strong enough, especially that by Orochi 2, after getting the humans to kick his ass, Masamune didn't even have his faith restored. I don't think he's Brainwashed and Crazy, he's doing it on his own will, which means he lost faith in humanity and would rather the world to BURN.
Wasn't there a dream stage in WO 1's Shu storyline, where Magoichi managed to get Masamune defect? Not to mention, Masamune was one of the characters shown fighting against Orochi in WO 2's intro scene...
I think its that Kiyomori Taira who is manipulating Masamune and storing some of the abyss in Masamune to keep him sorta Brainwashed and Crazy. Kiyomori has a large amount of arcane talents, including revival, simple zombification(if you believe that the ninja enemies in the Orochi army are undead), and the poison gas. Who is to say he didn't simply store some abyssal energy in Masamune to keep him going toward the goal. That goal, here is a wacky theory: Kiyomori was counting on the darkness breaking Masamune down enough that, once he revived Orochi, he could simply use Date as a tribute to fully revive Orochi due to the strength of Masamune's soul. However, Himiko negated all of that and at the end all we are seeing is another embodiment of chaos. Nothing remains of the original at that point, Shin Orochi wiped it clean out due to the fact the original Masamune was too weak
All this makes it seem that KOEI just simply hate Masamune and wants him to be the token 'ObviouslyEvil Overlord' of Samurai Warriors just like Dong Zhuo (Fuuma wasn't a warlord). The only thing that could break him is for an additional Date officer to be included in Samurai Warriors 3, and subsequently getting carried over to the third Orochi series. However, judging with how it looks, KOEI seems to have no intention for that and is satisfied for having him the villain.
Actually, one thing Masamune says when he refuses to join you in Orochi 2 kind of hits me as Fridge Brilliance. He pretty much says that after they defeated Orochi the first time the new world collapsed into random factions battling each other just like how it was before Orochi showed up and believes Orochi is the only one who can put an end to the constant fighting. This means he's gone Well Intentioned Extremist .
Actually this Character Derailment was a Take That! to Capcom and it's series Sengoku Basara who's posterboy is Masamune after one of their games insulted Yukimura and one thing you don't do to Koei is insult one of their posterboy's.
May be wrong, Masamune-Yukimura rivalry in BASARA reaches Ho Yay level. The one thing that irked Koei is that Capcom made Kanetsugu (who appears first in Basara 2), into Joke Character per excellence who constantly boasts he's invincible. Kanetsugu was one of Koei's dear boys (aside of Yukimura and Mitsunari), thus they didn't take it well and took the two poster boys of Basara in the second game who's not Yukimura (Masamune and Keiji) into Orochi's underlings. Do note that Warriors Orochi is released after Sengoku Basara 2.
Or... the reverse. One thing you don't do to Capcom either is insult one of their poster boys, this being Samanosuke/Akechi Hidemitsu, who's given a scene where Nobunaga kills him in Kessen 3. Which predates Basara 2.
The guy was always full of ambition like Nobunaga, Nobunaga knew that he will not settle for second place so he decides to work with Shu to boot out Orochi so he can be the ruling overlord of Japan.
WO3 solves this, it may be on ambition, but perhaps they could secretly understand that Orochi was probably just a Designated Villain so they see him as a worthy ally when everyone else (like especially Kanetsugu) was too blinded with the usual moral of "Never serve evil, or you're not a good person!". In hindsight, they might be right, because in the end, Orochi's consciousness turned into Shuten Doji, and he's not malicious, his power becomes Hydra, and they're not happy about it, and eventually, turns out Orochi used to be Ying Long, a decent mystic that got cursed.
Also, historically, Masamune was not exactly a trusted figure. He was ambitious and, shall we say, less than trusted by most. It's possible that this was a chance to really showcase that aspect instead of him being overshadowed by Nobunaga Oda
This one is more mythology based, but here's a headscratcher: given how Nu Wa is directly responsible for Da Ji being evil (in the myths, Daji was a fox spirit who, while mischievous, was fundamentally decent at first, but when exposed to the vileness of humans, she was corrupted into a brute, which means everything that happened afterwards was directly Nuwa's fault for being so bent on revenge towards King Zhou she ignored the long-term consequences of what she was going to do), why isn't she called out on it by Taigong Wang (which she was in the original story, as he blatantly stated that Daji was only partially responsible for her actions)? The mystic wasn't overly sympathetic of the goddess in the myth, and only beat Daji down because it was the right thing to do...
It's doubtful that WO!Nu Wa follows the classical Chinese mythology interpretation, since in that source, she is the creator of mankind, which should really make likes of Orochi the equivalent of a bug to her. But WO!Nu Wa is clearly, while still quite a badass Mystic, nowhere as powerful as her classical Chinese mythology self. Similar assumptions can be made for other Chinese deities.
It's called Sadly Mythtaken. It's common that stories don't follow mythologies by the book. Look at Disney's Hercules: they made Hera a loving mother and Zeus a benevolent god but in mythology, they're not good people (Hera's a jealous bitch who hates her husband's half-mortal bastard children while Zeus's a tyrant and a rapist). Same goes with Marvel's rendition of the Asgardians; Loki in the comics is Odin's adopted son rather than his blood brother. Koei's different interpretation of mythical characters is similar to how they interpreted the historical characters. So, it's not surprising that they made Da Ji a conniving bitch.