Kenji Koiso is a high-school nerd, but not one of those deplorable, wasteful otaku that the anime industry still wraps stories around. No, Kenji is a useful nerd: a math ace who almost represented his school in a national mathlympics. However, Kenji's still resigned to a summer spent debugging parts of Oz, the online nexus that essentially runs all the world’s computers and social networks. This would make for a boring movie, so Kenji’s perky classmate Natsuki Shinohara barges in and offers him a summer job at her family’s country estate.

Once out at the rural home, Natsuki reveals just what the job is: Kenji’s posing as her fiancé. Sakae Jinnouchi, the kindly matriarch of the clan, isn’t in the best of health, and Natsuki wants her grandmother to see her happily engaged. Kenji’s doormat personality and Natsuki-directed crush keep him from saying no, and he’s soon welcomed by Natsuki’s large family of fishermen, computer experts, defense-force soldiers, doctors, firefighters, and a second-cousin policeman whose fondness for Natsuki would be creepy if it weren’t played for laughs. Then another problem hits: someone hacks into Oz’s system, cripples the entire Internet, and frames poor nebbish Kenji for it.

So begins a spirited comedy of coincidences: the hacker is an experimental program called Love Machine, and it throws society into mild chaos by clogging highways, hijacking a satellite, and shutting down everyone’s email. Fortunately, Natsuki’s grandmother has friends in high places, and she calms things down with a few well-placed phone calls. And it so happens that Natsuki’s huge extended family includes Kazuma, a self-isolated kid who’s one of Oz’s top virtual fighters. And Natsuki’s black-sheep uncle Wabisuke, who crashes the big family get-together? Why, he’s the brilliant programmer who created Love Machine!

In the real world, half of the avatars in Oz would be giant talking sex organs.

Summer Wars has cyberspace battles to show, but it’s really about the lovable disorder of Natsuki’s family. In the face of social breakdown, they’re a bickering, close-knit bunch, and all of them come across as appealingly realistic, no matter how little time they get on screen. Hosoda handles all of it well, painting them with gentle amusement and foibles. Then, when the whole thing’s getting too cuddly, there’s a great loss. And Hosoda handles that with magnificent gravity, giving Summer Wars its best scenes.

But there’s still another story at work in the wilds of Oz. Summer Wars spares little effect in showing the vast online realm as a glittering virtual empire, from the giant-whale caretakers to Love Machine's ancient-death-god design. Oz is a stunning and surprisingly positive place, a cross between a spotless white Apple store and a version of Second Life where everyone’s a happy little animal instead of a giant blue Nazi werewolf dominatrix. It’s here that Kenji and the ranks of Natsuki’s relatives confront Love Machine, and it’s here the movie falters.

Hosoda is highly skilled at getting moments right in his films. It’s only the big picture that gives him trouble. Summer Wars goes in a dozen directions all at once, switching from Kazuma’s insecurities to the threat of nuclear war, and it doesn’t all fit. The climactic battles with Love Machine are played out with martial-arts fights, card games, and a duel of arithmetic, all stacked atop each other with breakneck energy. It’s all gorgeously animated and exciting, but it feels curiously hollow next to the movie’s quieter, stronger moments.

The whole of Summer Wars crystallizes in Natsuki and Kenji’s vague little romance: they’re cute, appealing, and just sorta thrown together. At first, Natsuki only likes Kenji because, well, he’s there, and Kenji only seems to like Natsuki because she is, as the film so annoyingly tells us, the prettiest girl in school. They drift together with a chemistry that’s subtle one moment and forced the next, driven on by Hosoda’s half-sweet, half-hokey message about how human connections are the only things that can save us. Like the movie itself, Natsuki and Kenji are endearing while their story lasts and hard to remember after it ends.

And let’s discuss that ending. Hosoda doesn’t know how to close the film properly, so he does it with a gag about nosebleeds. Know that anime staple where a fidgety male geek gets a huge spurting nosebleed from actual physical contact with a woman? Know how it’s trite and stupid and really an awful joke that was never funny in the first place? Well, guess what Summer Wars does after spending 110 minutes avoiding the majority of anime’s worst clichés.

Summer Wars still looks spectacular, and its excellent animation and soundtrack come through exceptionally well in FUNimation’s Blu-Ray release. The English version also scores many points with Michael Sinterniklaas as Kenji, sounding here like a less unhinged version of his Dean Venture voice. The rest of the cast are well fit, and anyone who insists on the original Japanese track will find little cause for complaint.

Gifted as he is at stealing Ghibli's wholesome thunder, Hosoda still needs a breakout film. A movie that vaults him from merely enjoyable work into the sparse ranks of truly great anime directors. A movie that does for him what Nausicaä of the Valley of the Wind did for Hayao Miyazaki and Millennium Actress did for Satoshi Kon. Summer Wars isn’t that movie. Yet it’s a fun ride, complex and charming and visually spectacular even when it’s bursting apart at the seams. Besides, it makes a math battle entertaining. That’s no small accomplishment.