Sorata and Arashi actually last pretty long in the movie (quite a feat), but there isn't a lot of their relationship in there. Sorata is a little more toned down, still flirting but not quite so... obviously. Arashi is also a little different- she's still quiet, but the "tone" of her quiet is a little more uptight ^^;;. Despite this, there is obviously a little something between them. It's more subtle than it is in the manga, but Sorata flirts and Arashi has something of a response. The vibe is almost like they had been "going out", but not to seriously.

Arashi and Sorata first appear near the beginning when the Ten no Ryu are sent by Hinoto to recruit Kamui. Sorata, like in the manga, calls Arashi "nee-chan", embarassing her (although I believe that this is changed to something a little vulgar in the dub, unless I am mistaken). There's a few little hints like this sprinkled throughout the movie....

The two are also "partners" of sorts in the movie. They usually fight together (such as their fight against Satsuki and Fuuma), and they seem to work together fairly well. Sorata obviously has the recklessness that's also present in the manga and anime- he gets hurt a few times helping out Arashi. While the two are fighting Satsuki, he gets a nice hole in his arm from a cable ^^;;;.

Near the end of the movie, Sorata and Arashi fight Fuuma. When Arashi gets hurt, Sorata takes him on and gets killed (naturally, we all know that Fuuma can't be killed by anyone other than Kamui u_u;;). While he's dying, he tells Arashi that he was happy to die if it was for her, and then wonders about her feelings for him. Arashi leans over and starts crying, and *squish* Fuuma, that coward, stabs her through the back with a comment of 'now she can tell you'.