Zenless Zone Zero: Their Hidden Past Story Quest Guide

To complete the "Their Hidden Past" story commission in Zenless Zone Zero, you must navigate the Hollow Deep Dive (HDD) surveillance grid, recover all three hidden Observation Data packets, and stagger the final Elite Ethereal during combat. Missing any data node forces a full stage replay to claim all Polychromes, as the commission ends immediately upon defeating the boss.

Roster Setup and Recommended Squads

Access the commission through the HDD console in Belle and Wise's workshop after completing prerequisite story milestones and obtaining Fairy's verification. Ensure your Agents meet the recommended commission level and equip suitable W-Engines and Drive Discs, such as Shockstar Disco for Impact scaling or Woodpecker Electro for burst damage.

A reliable squad requires an Impact-focused Stun Agent to fill the Daze gauge, a primary damage dealer to execute burst damage, and a Support Agent to provide buffs and responsive Defensive Assists. Pairing your squad with an aligned Bangboo grants passive team benefits and active combat support.

Squad Archetype	Core Agents	Recommended Bangboo	Primary Strategic Value
Shock Stun Squad	Anby, Anton, Rina	Plugboo or Amillion	Rapid Daze stacking and consistent off-field Electric damage
Physical Impact Team	Billy, Corin, Nicole	Bagboo	High burst during Stun windows paired with DEF shred support
Balanced Fire Core	Soldier 11, Ben, Lucy	Rocketboo	Reliable parries, defensive shields, and sustained Burn burst

HDD Board Routing and Observation Data

The HDD exploration board features locked security gates, terminal control points, and hazard tiles that rapidly generate Hollow Pressure. Excessive Pressure triggers Corruption Resonances that impose stamina penalties, reduced energy generation, or shorter dodge invulnerability windows.

Follow this sequence to clear the grid efficiently:

Activate terminal control switches: Clear security barriers before moving forward to avoid backtracking across active corruption spaces.
Cleanse Hollow Pressure: Step onto medical rest tiles and gear purification nodes before challenging locked encounter chambers.
Collect all three Observation Data packets: Thoroughly check side corridors and verify that your inventory shows three collected packets before entering the stage exit warp.

Elite Ethereal Combat Strategy

Combat encounters in this mission feature aggressive Elite Ethereals with fast multi-hit strings and forward lunges. Manage your defensive resources and stagger windows using the following tactics:

Parry on gold indicators: When an enemy flashes gold, activate a Defensive Assist to parry the strike, negate damage, and deal heavy Daze buildup.
Evade unblockable red flashes: Red flash indicators signal unblockable strikes. Use standard sprint dodges rather than Defensive Assists to clear the attack zone.
Preserve assist points: Do not spend assist points reacting to minor attacks. Conserve them for heavy combo starters so you are never caught without defensive options.
Maximize the Stun window: Once the target's Daze gauge fills completely, rotate through squad Chain Attacks, ensuring your primary damage dealer delivers the final blow.
Unleash pre-charged Ultimates: Build your Decibel rating to maximum before the enemy staggers, then activate your Ultimate immediately during the Stun window to maximize total damage.