Running on this one guess, any of Dante's actions in DMC 1 concerning the Phantom (whether as part of the story or optional through player intervention) can be seen in an entirely different light. Let's start with the beginning. Dante walks into the chamber with the Pride of Lion, and Phantom crashes in. We get a small exchange between the two. To paraphrase:
Phantom: I sensed something a little bigger. What a disappointing catch.
Dante: What a big surprise. I hope for your sake, you have something inside that big body of yours.
Phantom was only looking for food for its recently born offspring, and Dante goes ahead and calls her fat. No wonder Phantom got pissed enough to attack him. That's just in bad taste.
One boss fight later, Phantom is defeated and Dante obtains the Pride of Lion. Rather than go about his way to complete other tasks, he goes back into the room previous and slaughters Phantom's children. He leaves, and Phantom (justifiably mad by this point) chases him down the hall. He escapes, comes back, goes into another room and shoots/stomps more of her children then uses their blood to buy himself nice things.
One more hallway chase later, and Phantom attempts to end Dante for the last time. He, being the Jerkass that he is, tricks her into impaling herself on a statue and finally kills her. If that wasn't bad enough, the father Phantom shows up in the second game to get revenge, and Dante kills him too! All they were trying to do was feed their children, man, what a jerk.
- What must also be mentioned is Phantasmaranae, one of Bayonetta's summons in the game... Bayonetta. Has children, check. Is blatantly a female, check. The same species as Phantom, check. All of this is pretty much confirmed.
- Didn't Word of God say that Phantom was Phantasmaranae's child. That doesn't mean that Phantom is a female himself, it just confirms that Phantom's mother is Phantasmaranae. Also, Phantom has a male voice.
If you noticed her talking with Mundus, her eyes are shown red, meaning she is controlled by him into revealing her true nature when she didn't want to; otherwise, Dante would mouth off her, which he has done it. When Trish is captured, she is by her free will into
Taking the Bullet. Therefore, when she comes back to life, Trish is free to do what she wants, including siding with Dante.
Dante was on to Trish from the start
Dante knew Trish was a demon sent by Mundus from the start. That's why he never seems interested in why she just runs off after they get to Mallet Island, or how she can shoot lightning out of her hands, or why she looks like his mother. He's also not very surprised when she finally attacks him. He knew how suspicious the whole set up was, but decided to go along with it because why not? (He even purposefully brings Force Edge instead of Rebellion!)
This is what she's trying to Dante in mission 20 before he puts her at gunpoint; she's only doing this because Mundus told her. Now that her boss is dead, Trish is now sided with Dante.
Trish is Dante's mother, possessed by the soul of a lightning demon.
It would explain the resemblance. And just because someone's dead doesn't mean they can't be possessed. Perhaps Mundus put the soul in there himself. It would also explain her human form, which most (full) demons don't have - or if they do, it's just a disguise, whereas (as implied in the anime) Trish's human appearance actually IS her true form.
In a subversion of
Demonic Possession, Trish was
Killed Off for Real the first time but her body was conveniently left intact for Eva to transfer her soul into. With all of the body's previous powers in addition to her newfound powers of
LIIIIIIGHT (sorry, couldn't resist), "Trish" teleported conveniently to where Dante was facing off against Mundus, in order to aid her son. In the current games, she continues to keep up her appearance without explaining any of it to Dante, perhaps out of fear that he would devote himself more to protecting her rather than seeing her as a partner and putting his attention on world-saving. Or maybe he
just wouldn't understand.
- According to Mundus in Viewtiful Joe, Eva is possessing the amulet, and was responsible for not just Trish coming to back to life but Dante, as a child, which would explain why Vergil didn't try to find him - he may have seen the body.
