[TokuChris]

Okay!

So we learned in Episode 09 that it could appear that humans who are NOT Kamen Riders that eat the fruit from Hellheim forest turn in to advanced Inves monsters. We know this because we saw a sewer worker go to eat the fruit, and then only his helmet remained as a strange bat monster, that didn't like to eat our world's fruit, attacked people.

So let's go back to Episode 01.

Yuuya Sumii, the captain of Team Gaim, is given a Sengoku Driver from Sid. Yuuya immediately texts both Kouta and Mai to come see him - only he's not where he said he'll be, instead there's a portal to Hellheim. Kouta and Mai go through.

Kouta wants to eat the fruit but is snapped out of it from Mai's scream. Mai can stand perfectly next to the fruit and doesn't seem to give a damn. They find a Sengoku Driver laying on the ground - is it Yuuya's? A strange monster that is evolved from an Inves is coming at them. Could that be Yuuya, who ate the fruit?

It's important to note - the monster DID NOT ATTACK KOUTA AND MAI. It simply approached them and they ran away. It let out some weird blast when they were hiding from it, and then it approached Kouta again, but he attacked it - and thus it attacked back.

He turns in to Gaim - and as soon as he does, the monster goes ballistic on him.

During the fight, after Gaim has attached the swords together, the Hellheim Mai appears and says, and I quote (from Aeisr subs):

"Be warned."
"Your choice now will turn the course of fate."
"Continue down this path...and there shall be no turning back."
"You will have to fight until the bitter end."
"Till the world is dyed in your image."

Kouta responds, "If that's what it takes to protect you!"

Hellheim Mai then REMOVES THE LOCKSEED FROM THE SENGOKU DRIVER AND PUTS IT IN KOUTA'S HAND. The monster attacks, Kouta knocks him off the edge, and jumps after him. He looks back at Hellheim Mai, who points to something, and Kouta looks at his sword and realizes the lock fits on.

Then she is gone.

My theory? Yuuya is the monster. Yuuya did not attack them until he was attacked first. Once Kouta attacked, Yuuya defended himself. Hellheim Mai stopped him from killing the monster, even as far as taking the Lock Seed off the Sengoku Driver, telling him if he kills the monster, his fate is sealed. Kouta doesn't understand (MUST SAVE THE GIRL LOLZ) and keeps attacking the monster.

What was Hellheim Mai pointing at? I don't know. But Kouta thinks it was his sword. I don't think it was personally. Anyways, as soon as he connects the Lock Seed to the sword, Hellheim Mai is gone.

It's fun re-watching these eps now that we know more to the story.