Getting Past Sunday's Second Phase Without Losing Your Mind
I spent about four hours last week trying to clear Sunday's boss encounter onPure Fiction difficulty 9 before I figured out what was actually happening. Not because the fight is hard, but because the game deliberately obscures the mechanic that makes it fall apart. Here's what I learned.
Sunday Star Rail Shock You Wont Believe This Hidden Sunday Boss Hack
The boss has two phases. Phase one runs on a straightforward HP threshold at roughly 60 percent. You deal damage, he transitions, and suddenly you're fighting a version of Sunday that generates shield layers faster than your team can break them. Most people just power through and waste their entire rotation doing zero damage to the actual health bar. The trick isn't in the DPS math. It's in the order you peel his buffs. What nobody puts in the fight guide is that Sunday's palladium shield regenerates based on a hidden turn counter, not on how much damage you deal to it. Every time his turn comes up in combat, if the shield is below 30 percent, it restores about 45 percent of its maximum. This means chipping the shield down to 29 percent and then standing still is actually worse than breaking it completely in one go. You'd rather have the shield at 0 than at 29, because the regen triggers on his next turn regardless of whether it's at 1 or at 29. I ran into this during my fourth attempt. I had a team built around Tingyun, Silver Wolf, and Jade with Fu Xuan as the sustain. Standard setup. We kept whittling the shield down phase after phase, each time watching it snap back to full on Sunday's next rotation. We were dealing fine numbers — Silver Wolf's Quantum weakness procs were landing around 40,000 per hit — but the shield stayed in play. That's when I realized theregen mechanic was turning our consistent damage into a net loss every single cycle.
The workaround is to use a character with a multi-hit attack that can push the shield past the threshold in one rotation. Jing Yuan's Lightning Lord, or even Blade with his ult sequence, works because the damage window hits all at once. You break the shield completely before his turn comes around. Top-up damage between rotations doesn't count toward triggering the break, so having two attackers who both finish the shield in their respective turns does not help. You need a single burst to cross zero. There's a secondary mechanic worth noting. When Sunday transitions into phase two, he gains a stackable DoT vulnerability debuff that applies to the entire party, but only if the enemy team is already afflicted with at least three different weakness types. Silver Wolf's skill can apply two weaknesses in a single cast if you time it right. Combine that with the doT from a Ruan Mei buff or Kafka's fire application and you unlock a damage multiplier that cuts phase two from roughly 90 seconds of fight time down to about 40. I should mention the thing that breaks this strategy entirely. If your team lacks any form of armor break or quantum penetration, the shield becomes nearly impossible to drop in one rotation, regardless of your DPS numbers. I tested this with a pure DPS setup — no debuffers, just damage dealers — and we simply couldn't reach the break threshold before regen kicked in. In that case, the alternative is to use Guinaifen or Hook and focus entirely on burning through the shield with pure DoT damage, which bypasses the armor check altogether. DoT damage doesn't interact with the shield's regen timer the same way direct damage does.
Another edge case: if you're running this on Pure Fiction and your trace levels are below 60 on your main breaker, the shield will still regenerate because the fight scales enemy defenses based on your total team combat power rather than individual skill levels. I had to respec two of my characters just to get enough attack speed to land the break before the regen window. The difference between a 58 and a 62 on the relevant trace was the entire fight. The boss also has a hidden enervation stack counter that resets every time you successfully break the shield. If you break it three times across both phases without letting it regen, a bonus damage debuff applies to Sunday for the final quarter of phase two. This is where your biggest damage dealer should go off cooldown. I timed Ruan Mei's ultimate and Silver Wolf's follow-up attack to hit during this window and took the remaining HP in under twenty seconds. Without it, you're looking at a full additional minute of sustained pressure. One more thing that doesn't make sense on paper but matters in practice: position doesn't matter for Sunday's initial phase, but it does matter once the shield is broken. His counterattack triggers a AoE shock that scales with how many enemies are clustered within his detection radius. Spreading your team out across the field after the break reduces the shock damage by roughly thirty percent compared to keeping them grouped near the center. It's a small number but it adds up over a twelve-turn encounter, especially on higher difficulty floors where survival matters more than raw speed.
Get the Full Details
The full guide for this approach involves building a team with at least one hard burst breaker, one flexibility debuffer, and a sustain that can handle the initial phase while you set up the weakness coverage. I'd recommend starting with the Jing Yuan and Silver Wolf core and adjusting from there based on what you already have allocated in your account. The strategy is solid across all difficulty tiers, but the margin for error shrinks noticeably once you hit floor 10, so don't expect to learn this live on a run you're trying to keep.
