Can You Unlock Zuo Ci in Dynasty Warriors 5 (PS2)? No — He Debuted in DW6

No. Zuo Ci was introduced in Dynasty Warriors 6. He does not exist in Dynasty Warriors 5 on any platform.

Characters with Healing/Support Abilities in DW5

• Zhang Jiao: Musou attack restores health to himself and nearby allies.
• Cao Cao: Certain attacks (varies by weapon/move set) can heal allies while damaging enemies.
• Zhurong / Zhu Rong: Fire-based movesets; some iterations have self-sustain.

If you want to play as Zuo Ci, you'll need Dynasty Warriors 6, 7, 8, or 9 (or Warriors Orochi series where he appears).