[The Green One]

Spoiler for Comparison to the manga:

The Fiore subplot has apparently been cut completely as part of an effort to save time. Which is acceptable enough as the story is almost unaffected without her. Just some minor alternations and everything flows as normal.

Keima is a socially withdrawn person who normally does not interact with people much. So when pursued by an aggressive girl I think it would make sense that he gets thrown off his pace and can't respond the way he wants to. Though Imperial's theory is plausible too.