Kingdom Hearts II "Ansem" talking to Ansem?

Spoiler

Can anyone help me understand why Ansem, Seeker of Darkness it talking to DiZ(Real Ansem) in the beginning of the game. I don't understand why they are cooperating and I couldn't find any information on wiki on this. It's clearly "Ansem" and not Xemnas. When DiZ asks for his name he says Ansem and DiZ laughs irionically. It appears that "Ansem" lost his memory etc? I don't know. Or is it simply Riku in Ansem form and when and why does he return to normal form

 

no diz was acually speaking to rikue ansem seeker of darkness form cause if you play days you find out that ansem is still in rikue and rikue uses this power to deafet roxas but is stuck looking like ansem. so it was riku the whole time.

 

It was Riku in his Ansem form which may have been his Dark Form's new...form.
He took the appearance of Xehanort's Heartless to use the darkness to fight Roxas or something.

I'm not entirely sure on this, but if I remember correctly, his memory was still fuzzy because of Chain of Memories and he called himself Ansem because he was disappointed with himself or something for using the darkness.

 

I'm pretty sure that Namine never did anything with his memories while he was in Castle Oblivion since they kinda didn't know he was there since he just appeared in the basement out of nowhere. I forget how he got there or if it ever was explained.

As for why he looked like Ansem, it's because he had to use the darkness to defeat Roxas after he left the Organization in order to bring him to DiZ. Using the darkness caused him to look like that for some reason that slipped my mind.

 

It was Riku. He just looked like Ansem cause he had to use his dark powers to defeat Roxas. He looked like Ansem cause Ansem's darkness was still inside him.

 

The "Ansem" you are referring to is

Spoiler

Riku, who at that point took on the form of Ansem to capture Roxas and awaken Sora. If you played through this game or Days you would have realized that. In CoM he's fighting with the real Ansem and though Riku defeats him he's still in his heart. He awakens the power of darkness inside him by taking on the form of Ansem in his fight with Roxas because he is losing and thinks that Sora and Roxas must be together for Sora to wake up.

You really should've played through the game before asking this because the answer becomes more clear as you go through the story.