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In Tokyo's ritzy Roppongi neighbourhood, Tsunekazu Ishihara, president of The Pokémon Company, sits opposite a giant map of the world.

Red pins mark the countries where every arm of the Pokémon empire - games, trading cards, Pokemon GO, the animated TV series - is available.

There's a lot of red.

Pokémon started life as an 8-bit video game in Japan - where players capture creatures and store them in pocket-sized capsules (Pokémon is short for "pocket monsters") - but has grown into a cultural megahit.

By some estimates, Pokémon is now the biggest media franchise in history, worth more than Harry Potter and Star Wars combined.

Over its 25-year journey, it has spawned several global crazes, involving celebrities paying millions for trading cards and people walking tens of thousands of kilometres in pursuit of rare monsters.

These are the moments when Pokémania swept the globe.

Pokémon started small. The game's developer, Game Freak, was a Tokyo-based company that had started life as a self-published video gaming magazine.

"It took about seven years to develop the games. We thought they would sell well in Japan, perhaps a million copies of each," says Mr Ishihara, who was part of the original games' development team.

He turned out to be right. The series' first instalments, Pokémon Red and Green, were released in Japan on 27 February 1996. They proved popular, with players using cables to link their Game Boys and trade for certain Pokémon that were exclusive to each version.

"But we never considered selling Pokémon abroad," Mr Ishihara says.

"People said there was no chance it would work because American children wouldn't play a game where you had to read a lot of text, where there was no action and where you took turns to fight battles."

Pokémon Red and Blue - based on an updated version of the Japanese originals - were released in North America in 1998 and in Europe in 1999. They were followed by Pokémon Yellow, Gold, Silver and Crystal.

"All told, they sold 76 million copies worldwide. I was absolutely shocked," Mr Ishihara says.

Mr Ishihara believes that the tortuous process of translating the games into English was part of the success, with the North American release of the anime building hype for the delayed Game Boy games, which in turn fed demand for a newly-launched trading card game.

"As we launched more and more products and expanded the business, it became a social phenomenon," he says.

At its height in the early 2000s that phenomenon - branded "Pokémania" - led religious leaders in Saudi Arabia to ban Pokémon entirely, saying the game promoted Zionism and gambling, while western media published lurid stories of "Pokémon card crime".

There was some truth to the stories: in one incident, an eight-year-old boy in southern England caused an outcry after he phoned in to a local radio station and attempted to swap his infant sister for a holographic Vaporeon card.

Although this wave of Pokémania died down in the years that followed, Pokémon never went away.

2008 saw the launch of a new generation of WiFi-enabled Pokémon games. Suddenly, players could trade and battle with anyone, anywhere.

"As a kid, I watched a lot of people battle on WiFi battles in 2008, that's when that really blew up on YouTube," says Aaron Zheng, who started a YouTube channel focused on competitive Pokémon after coaching his younger brother to victory in the games' world championships in 2013.

The channel led to work commentating at official Pokémon tournaments, taking Zheng from his home in New York to Australia, Brazil and the UK.

"The cool thing about Pokémon is it's a really global game. I think if I went to a big city, there'd probably be someone that I know from Pokémon that I could probably crash with. I think that's so cool," he says.

On 12 February 2014, a channel on the streaming service Twitch began an experiment.

The channel, "Twitch Plays Pokémon", broadcast a stream of Pokémon Red. What was different was that viewers could play the game, interacting with it live by typing commands into Twitch's built-in chat.

"I think Twitch served as sort of that perfect platform. You've got the video, you've got the chat, it was right for something like that," says Marcus "djWHEAT" Graham, a long-time esports expert and head of creator development at Twitch.

"The streamer's original system fit perfectly, like, yeah, throw me the commands, I'll begin parsing them into the game and we'll see what chaos this creates," he says.

The chaos was compelling. More players joined in, thousands of people telling the game to do different things all at the same time.

Twitch Plays Pokémon went viral, gaining widespread media attention within days. According to Twitch, the stream's peak saw over 120,000 simultaneous players trying to control the action.

The sheer number of players sometimes made the game almost impossible to play. At one point progress was held up for almost 10 hours as players repeatedly fell down a ledge, while stray button presses in an in-game menu caused some of the stream's most beloved Pokémon to be "released", meaning they were lost forever.

But after 16 days, seven hours, 45 minutes and 30 seconds of play, the stream completed the game. In all, 1.16 million people had played, and more than nine million had watched.

Marcus Graham believes the "Pokémon" part of Twitch Plays Pokémon was the key to success, as the stream combined the simple goals of catching monsters and collecting gym badges with players' nostalgia for the classic game and its cast of familiar characters.

"I really do think that because the game was Pokémon that played a massive part in the explosive virality of it all. It was kind of that perfect storm."

While the world watched millions play Pokémon Red on Twitch, a Japanese software engineer was working on an April Fool's joke.

Tatsuo Nomura (who declined to be interviewed for this article) worked for Google's maps division. A Pokémon fan since childhood, Nomura decided to blend the two, hiding Pokémon on a map of the world for users to find.

"Mr Nomura used to find exploits in Pokémon Red and Green when he was a kid, that's how he became interested in computer programming," explains the Pokémon Company's Tsunekazu Ishihara, who greenlit the project after receiving a pitch from Google-owned game developer Niantic.

"That passion led him to join Google, then Google Maps, and consequently he created Pokémon GO."

The mobile game was an instant success, introducing millions of players to a world of "augmented reality" gaming. To play, users must walk around in the real world in order to find and catch Pokémon on their phone screens.

One Japanese player, playing under the name Kyarorina, got hooked after his workplace organised a walking competition for its staff.

"The goal of simply walking turned into an obsession with chasing after rare Pokémon and catching them all," he says.

The stats tell the full story: since first downloading Pokémon GO in July 2016, he has walked over 31,000km (19,200 miles) and visited more than a million Pokéstops - real-life locations where players can collect in-game items.

In 2019, Kyarorina became the first person to catch one million Pokémon in-game.

"Recently I've been spending about eight to 10 hours a day catching Pokémon, about 2,000 a day. I think I'll hit two million by the end of this month and announce it on Twitter," he tells the ´óÏó´«Ã½.

Pokémon GO's initial popularity was matched by its profitability. In 2020, five years after the game was first released, it saw record revenues of over $1bn (£718m). The free-to-play game makes money both by charging players for items and by charging businesses for the privilege of appearing on the in-game map.

For Neriko Doerr and Debra Occhi, cultural anthropologists who co-authored a book on Pokémon GO, the game is evidence of Pokémon's broad appeal - something that can help explain the franchise's success.

"Pokemon GO attracted people who are into going outside, walking around and people who are happy with just collecting Pokemon into the game world, some of whom became very enthusiastic," Ms Doerr says.

As Pokémon's 25th birthday approached, the franchise once again hit headlines as YouTuber Logan Paul paid $2m for six boxes of vintage Pokémon cards.

"This is a newfound obsession of mine and I am so excited to share it with other enthusiasts around the world," the controversial entertainer wrote on social media.

"Pokemon cards have always been highly prized," says Tracy Martin, an expert in valuing post-war collectables.

"This is down to nostalgia and obviously the rarity of a card, but also Pokemon is still very current. It's a phenomenon that seems to grip both children and adults, and that's the main reason why it's still going strong," she says.

"That was not what we expected," says Pokémon's Tsunekazu Ishihara, who was himself featured on a Pokémon card that last year sold for $50,000.

So what does Ishihara expect the next 25 years will bring for Pokémon?

"World domination" he says, eyes fixed on the red pins that dot his map.

Additional reporting by the ´óÏó´«Ã½'s Sakiko Shiraishi.