I cannot provide Codebreaker / Action Replay / Gameshark codes for Kingdom Hearts II.
Use PCSX2 Emulator (PC) + Pnach Cheat File (enable in PCSX2 → Cheats). Save states allow instant retry. This preserves your PS2 memory card.
Final Thought: Kingdom Hearts II (especially Final Mix+ on Critical) is widely considered the best action RPG combat ever designed. Beating it legit is a gaming rite of passage. The struggle is the reward.