Open Wide Rex! Dangerous X!

"There's something I'd like to ask of you, Ichinose." Houtaro is asked by Rinne, who has a thoughtful look on her face, to confide in him about a certain problem of hers. Just what exactly is on her mind? Then the two are dispatched to the appearance of a new Level 10, X-Rex. Houtaro and Rinne attempt to tame it but encounter a little girl instead...