Recently the great Japanese tradition of having mascots called yuru-chara to represent cities and other institutions has been gaining more and more overseas attention. A particularly attention grabbing character is Chiitan the otter, an unofficial mascot of Susaki city.

Since the character’s inception, Chiitan has been a chaotic force on social media, posting dangerous and bizarre challenges, resulting in over 1 million followers on the Chiitan English language Twitter page.

Despite their differing personalities, Chiitan has been an associate of Shinjo-kun, the wholesome official mascot of Susaki city. Previously, Shinjo-kun has even won the Yuru Chara Grand Prix, the highest honour for a Japanese mascot, and he is everything that is expected of a cute yuru-chara.

From time to time, Chiitan has even dragged a seemingly unwilling Shinjo-kun into the provocative hijinks.

In a recent controversy, Susaki city 'fired' Chiitan, and Shinjo-kun was told to stop associating with the chaotic mascot. Chiitan could be seen as a bad influence and the outrageous stunts were giving Susaki city a bad name.

In a segment on Last Week Tonight, an American TV show hosted by British comedian John Oliver, Chiitan and Shinjo-kun’s fraught relationship was explained, and Oliver himself offered a solution. He created a new character which fused his own likeness with that of Chiitan, a mascot called ‘Chiijohn’. Chiijohn was then sent to Japan to meet his new best friend in a hilarious clip.

According to the narrator of the clip, being friends with Chiitan was ‘a f--king nightmare’ and Shinjo-kun is happy that he and Chiijohn can hit moles in arcade games instead of each other.

The two seemed to hit it off straight away. But if you think Chiitan would let his best friend be stolen that easily by some TV comedian, you’ve got another thing coming. He posted this fiery tweet which directly challenges John Oliver to a no holds barred fight.

The challenge references one of Oliver’s earlier segments about WWE in which he got obsessed with the phrase ‘explode through a table’, the tweet also calls him ‘Mr. British Birb’. That’s some fighting talk.

John Oliver also retweeted the aggressive callout and seemed to relish it. He said, ‘I’m in a public beef with an unsanctioned Japanese otter. I needed this.’

If you're interested in Japanese mascot antics, check out 8 of the most bizarre mascots in the country. Otherwise you can probably follow the transnational, trans-species beef's progression on Chiitan's Twitter page.