The movie begins with our young protagonist, Haruka, being read a children's fantasy by her bedridden mother. The book tells a story of a man whose treasured comb was returned to him by a fox after offering an egg at a shrine. The townspeople begin offering eggs to the shrine in hopes of having their items returned as well, but little do they know that the foxes are actually responsible for stealing the items that are considered 'forgotten' by the people. Haruka assures her mother that the hand mirror she received as a present won't share the same fate, since she'll treasure it forever.
Flash ten years into the future, where Haruka is now a teenager. Her mother is no longer around, and she seems unsatisfied with her workaholic father and her disinterested friend. For a change of pace, she visits the shrine to pray for her hand mirror to be returned, since, as expected, she forgot about it and subsequently it had been lost.
Haruka falls asleep at the shrine and wakes up to a scrounging fox-like anthromorph. The fox grabs some stray items, including Haruka's keychain, and scurries off. Haruka follows the creature into a parallel dimension, where the fox panics and tries to disguise her, or else he could get into trouble for leading a human to their world. After escaping danger, the fox tells Haruka to return to the human world, but she insists on staying to look for her mirror.
Haruka promises to give the fox, who introduces himself as Teo, her keychain if they find her mirror. He agrees and they set off to search for it. On the way, Teo is bullied by three street-gang members, and Haruka helps him get away. The bullies guess - correctly - that Haruka is a human, so they head off to expose her.
There's a pointless scene where the bullies chase Teo and Haruka which leads to the only funny moment in the movie, where their cylindrical vehicle flies off a roof, lands sideways on a tower, and slides down it, like a ring-toss game at a carnival. Teo and Haruka escape to a theater that is performing a play with one of Haruka's forgotten toys - don't ask why - and the bullies bust in, despite not knowing that their targets were in the theater. Haruka reunites with her toy, named Cotton, and the bullies chase her while causing a lot of property damage, even though she had already revealed herself to be a human, which calls into question the bullies' motive for chasing them in the first place.
The duo escapes and retires to Teo's house, where Teo reveals that the mirror is in a underground thieves lair - why he doesn't reveal this earlier when they're searching for the mirror is anyone's guess. Teo then steps outside where he's kidnapped by the evil Baron, who tells the fox to use Haruka to get back the mirror so that he can steal it. Of course, Teo will be rewarded handsomely.
The next day, the pair travels into the lair and the movie is tragically cut short when their cart derails and a giant stuffed monster forces Haruka into a pit of lava, killing her instantly - that is, until the lava is revealed to be syrup. The teenager climbs out and rips the stuffing out of the monster to discover that her mirror is inside of it. She retrieves the mirror and attempts to escape with Teo, but they are headed off by the Baron, who kidnaps Haruka to be a slave and steals the mirror.
The Baron reveals his plan to use mirrors to control a robot army (mirrors are like a power source), and then proceeds to administer an amnesia gobstopper to Haruka by means of a Rube Goldberg machine. This gives Teo ample time to sway the townspeople into committing treason against the Baron, and they use Teo's reward money to build a plane that will propel him to the Baron's dirigible.
Meanwhile, Haruka's toy, Cotton, rallies an army and inexplicably boards the Baron's airship without having any means to do so. The baron dismembers the sentient toy, and Haruka escapes into Teo's airplane. Then, amidst cannonball fireworks and balloons, Teo's airplane crashes into and disables the Baron's airship. The film then goes into a metaphysical sequence which explains the moral of treasuring memories, after which the Baron is defeated and Haruka retrieves her mirror and returns to the human world.
So that's Oblivion Island. Haruka and Teo are the only characters who have more than a few lines, the plot is full of holes, and the story, for the most part, is unoriginal. For a children's movie, Oblivion Island is not charming, interesting, or funny. There are no attempts at puns or jokes at all, and since there is hardly any gripping drama, the movie ends up being a sort of fantasy adventure - the kind you might see if you had a high fever. However, the visuals are absolutely stunning, essentially making the art and animation the only attractions of the film.
