It didn't happen much after this week when they first met, but Araragi used to make Hanekawa's heart flutter and fluster her in amazingly cute ways.
The 2nd movie is all about Araragi defeating the three vampire hunters to gain back Heart-Under-Blade's limbs. Hanekawa kept showing interest in Araragi, but he tried to drive her away because of his new monster nature and having to deal with other monsters.
His first battle ended well, only because he studied a book on baseball instead of Aikido.
Hanekawa saw the fight and realized why Araragi was being so mean. She offered to show her panties, and more, so he would accept her help, but for Araragi, the panties were enough.
When we got to the TV shows, it was already Heart-Under-Blade's thing to just eat monsters to eradicate them. Eating was just how she solved her problems. In the timeline of this movie, it was the first time Araragi saw how good Shinobu was at "eating" things.
Heart-Under-Blade took back her leg and then she got a little bigger. She's gone from a grade schooler to a middle schooler. Having sisters the same age made him all excited to see a new one.
This one week vacation dealing with vampires was when Hanekawa and Araragi fell in love. Really in love. I'm really curious to see how this budding romance got changed into something he had to leave behind before he met Senjougahara. Yes, Hanekawa realized it was her fault he had to go buy an ecchi mag because she showed her panties and flirted with him the afternoon before.
After we saw how Episode the half-vampire fights, we now know why Araragi hates him so much. He almost killed an innocent human girl in Hanekawa. But her analysis of how Episode works let Araragi defeat him and get Heart-Under-Blade her other leg. She went from middle schooler to high schooler. She's almost back to her adult form!
Hanekawa and Araragi's last visit before his last fight established all the stakes necessary for the hopes dashed in a tragic fall. With each fight, Araragi had to give up more and more of his humanity to win and to save Hanekawa's life. Not even the courage of her loaned out panties could prevent her from being kidnapped and setting up the cliffhanger for the 3rd movie. What happens in that part of the story closes forever whatever loving relationship they could have had. It's a bittersweet anticipation to see how it all unfolded.