Two cats that have spent the past two years trying to enter an art museum in western Japan – only to be politely turned away at the door – have become online celebrities with a global following willing them on in their attempts to see at least one exhibit up close.

Ken-chan, a black cat, attempted his first solo foray into the Onomichi city museum of art in summer 2016 during an exhibition of cat photography, but was prevented from entering by a security guard in a gentle standoff that was caught on camera.

“I’m guessing that Ken-chan spotted some of the exhibits through the glass, and since the photos included those of black cats, he must have thought he had found a new friend,” the museum’s curator, Shinji Umebayashi, told the Guardian. “And then he just kept coming back.”

Not to be deterred, Ken-chan started turning up accompanied by a ginger cat the museum staff named Go-chan. “I’d seen him around so we think he must live locally, but we’re not sure where, exactly,” Umebayashi said.

Ken-chan has struck up a friendship with the museum’s security guard, who playfully sends him on his way whenever he attempts to cross the threshold.

A post on the museum’s Twitter account from last month shows Ken-chan waiting patiently outside before making a bid for the entrance as the automatic doors begin to close. The guard springs into action, keeping his friend out of harm’s way.

Photographs and video clips of their exchanges have gone viral. Some people on social media have implored the museum to allow Ken-chan in. Most, though, are just charmed by the interaction between the guard and his feline friend.

The museum, which has more than 45,000 Twitter followers, recently launched a range of souvenirs featuring the two cats, but is struggling to keep up with demand amid a rise in visitors and orders sent via social media.

Ken-chan and Go-chan, who continue to visit “most days”, are often seen together in the museum grounds, said Umebayashi, adding that despite both being male, they have never exchanged so much as a hiss. “The museum is in a park so there’s no traffic to worry about,” he said. “They treat the park like it’s their own garden.”

Even though Ken-chan’s feline cunning is unlikely to outsmart museum staff and gain him free admission, as the resident cat at a nearby restaurant, at least he does not have far to walk home after yet another foiled attempt.