The Massacre in Tokyo was a planned mass murder carried out by Clint Barton and aimed at executing the members of a Yakuza faction led by Akihiko.
In 2018, Clint Barton was ridden with guilt after his wife and his three children were all killed during the Decimation.
In the five years that passed, Barton decided to take up a life of vigilantism, serving justice to those who weren't killed by Thanos. After killing a cartel gang in Mexico, Barton made his way to Japan, where he tracked down an active Yakuza faction in Tokyo led by Akihiko.
Planning to eliminate all members of the Yakuza faction, Clint Barton began to fight against them, despite their great numbers and rapid gunfire. Barton managed to make his way through all enemies with great ease, going through a building where he headed for Akihiko, a Yakuza operative. The two then found themselves in the streets, where Akihiko questioned Barton on his actions, which he informed him that they survived the Decimation and half the population didn't.
As their the duel began to settle down, Barton was able to cut Akihiko twice, causing him to beg for his life, and promising to give Barton anything he wanted.
However, Barton ignored Akihiko's cries for mercy, stating that the only thing he wanted, which was his family, could not be given by him. Barton then finished off Akihiko and cleaned his sword of Akihiko's blood.