As far as characters go, Hina already looks like she can be used as more than just background eye candy, and while I love Ryotarou to bits, all of us are pretty much calling Eiji "Ryoutarou done right."
Ehh, I'm iffy on Hina. We saw Hanako strongarm the Imajin plenty in early Den-O, yet she didn't really amount to anything as female characters in Rider go. I would consider her less useful/interesting than Sakurako, even.
Now, maybe that's because of circumstances forcing the Hanako -> Kohana transformation. I'd still want to see some demonstration of integrity or self-motivation on Hina's part before I can believe her physical strength translates into strength of character.
As for the "Happy Birthday" stuff, all it made me think of was this: