Shiyu Defense — Zenless Zone Zero

Shiyu Defense is a Game System and a periodic military operation organized by the New Eridu Defense Force. Its primary objective is to defend inert-type massive Ether-storing constructs known as "Shiyu Pillars" located within Hollow Zero and to annihilate enemies attracted by the substantial amounts of Ether matter within the Shiyu Pillar.

Since Version 2.5, in order to unlock Shiyu Defense, the player needs to have reached Inter-Knot Level 35, been promoted to "Certified Proxy," then have completed the main side quest "Shiyu Defense (Commission)". (The original pre-2.5 requirement was progressing through the Main Mission "Chapter 2 - A Call From the Hollow's Heart".)

Shiyu Defense is a high-difficulty challenge stage where you must defeat all enemies within a limited time to complete the challenge. Stable Node is unlocked one by one as you progress through the challenges, and does NOT refresh. Starting at the Seventh Frontier, players must build 2 separate teams to enter the challenge and clear the stage.

Disputed Node is likewise unlocked one by one as you progress through the challenges and does NOT refresh, like Stable Node. Per the the community wiki Change History, Disputed Node was added in Version 1.1. Unlike Critical Node's time-based scoring, Disputed Node has NO time limit — your grade depends entirely on character survival: if none of your characters are knocked out during the stage, you collect the full reward.

Critical Node periodically updates with new stage content, refreshing every 15 days — this is the most frequently rotating sub-mode among Shiyu Defense's four. Critical Node's highest tier — tier 5 — is made up of 3 separate stages within a single cycle, each usually requiring a different squad, making it the tier that demands the most team compositions in all of Shiyu Defense.

Ambush Node is not currently available. Per the the community wiki Change History, it was added in Version 1.2 and then removed in Version 1.3. While active, Ambush Node was available for 30 days. While it was active, Ambush Node's scoring worked like Disputed Node: NO time limit, graded by how many Agents were defeated — if no Agents were incapacitated during the stage, you collected the maximum reward.

the community wiki notes that clearing each stage grants rewards of different tiers based on completion time, including Polychrome and Master Copies. The page also lists 9 Achievements related to Shiyu Defense, some of which reference "S-Rank"/"S+ rating"/"A-Rank" ratings — showing a per-stage rating system EXISTS, but does not publish the exact formula or weighting (time/combo/damage) behind that rating. The community analytics page originally planned as a cross-reference source returned a genuine 'Page Not Found' error at the time of this research, so no analytics data was available either. Detailed scoring mechanics: not yet published. (Critical Node's exact point thresholds and time-based multiplier are detailed separately in the two sections above — 'Time-based score multiplier' and 'Grade thresholds'; the precise conversion rate from raw damage dealt to Damage Score points remains: not yet published.)

In Critical Node, both DMG Score and Elimination Score (earned per normal/elite enemy defeated) receive a multiplier based on how much time remains when they're earned — the earlier you earn them, the higher the multiplier: ≥4:00 remaining ×5 · 3:59-3:50 ×4.2 · 3:49-3:40 ×3.5 · 3:39-3:30 ×3.0 · 3:29-3:15 ×2.5 · 3:15-3:00 ×2.0 · 2:59-2:45 ×1.6 · 2:44-2:30 ×1.3 · ≤2:29 ×1. For example: defeating 1 elite enemy grants a base 500 Elimination Score, but defeating it before 4 minutes remain multiplies it 5x to 2,500 points. The total score for a room (including the multiplier) is hard-capped at 50,000 points.

Critical Node's overall grade is derived from each room's grade: reaching S-Rank in ALL rooms earns the overall S Grade; A-Rank in all rooms earns overall A Grade; B-Rank in all rooms earns overall B Grade. S+ Grade specifically requires BOTH an S-Rank in every room AND a combined Critical Node score of 100,000 or more. Per-room point thresholds (general): S-Rank from 25,000 points, A-Rank from 18,000 points, B-Rank from 8,000 points. The hardest content — Critical Node tier 5 — uses a lower A-Rank threshold: A-Rank from 16,000 points (S-Rank and B-Rank remain 25,000/8,000).