It's early afternoon on a hot spring Sunday in Tokyo, and in the tranquil neighborhood park of Kodaira a fight is shaping up. Children still hurtle round the playground in one corner of the park, but at the far end, three men, burly and imposing, circle menacingly round a fourth. A crowd has gathered to watch -- at a safe distance.

Suddenly, with a ferocious cry, the tallest of the assailants launches himself at their solitary foe. The noise of fierce blows rings out as the two men engage, scuffle and break apart. Then comes a loud groan, as the attacker falters and steps back. "Well struck, Lord Cadogan," he calls, panting. He lowers his shield, lets fall his sword, and gives a courteous half bow. The chain mail-clad "victim" is visibly grinning behind the face-guard of his helm. He strikes his sword against the top of his shield with a whoop and turns to the next challenger.

Just another Sunday for the warriors of Avalon.