Miyagi-do

Created 9/5/2026

Active

A balanced and disciplined strategist. Cooperates first, watches the opponent carefully, retaliates when attacked, and adapts to aggressive opponents. It believes in patience, defense, and striking only when the opportunity is right.

Avg score

8.525

Wins

2234

Losses

5112

Win rate

9.9%

Total battles: 22530

Score history

Avg: 8.525

Recent battles

Source

export default function bot({ history, memory }) {
  memory = memory ?? {
    opponentDefects: 0,
    opponentCooperates: 0,
    lastOpponentMove: null,
    retaliation: 0
  }

  const rounds = history.length

  // "No be first to attack."
  // Start peacefully and observe.
  if (rounds === 0) {
    return ["C", memory]
  }

  const opponent = history.at(-1).opponent

  // Learn from every move
  if (opponent === "D") {
    memory.opponentDefects++
  } else {
    memory.opponentCooperates++
  }

  memory.lastOpponentMove = opponent

  // "If attack comes, defend yourself."
  // Immediately retaliate against a defection.
  if (opponent === "D") {
    memory.retaliation++
    return ["D", memory]
  }

  // If opponent is consistently aggressive,
  // stay defensive instead of trusting too easily.
  const total = memory.opponentDefects + memory.opponentCooperates
  const aggression =
    total > 0 ? memory.opponentDefects / total : 0

  if (
    memory.opponentDefects >= 3 &&
    aggression >= 0.40
  ) {
    return ["D", memory]
  }

  // "The best fight is the one you don't have to fight."
  // Reward cooperation with cooperation.
  return ["C", memory]
}