Bullet Hell

What it is. A shoot-‘em-up where the screen fills with coherent bullet patterns the player threads on foot. The bullets are the level; your hitbox is a single pixel; the whole game is reading density as motion.

Player fantasy / why it’s fun. “I walked through a wall of death and it was gorgeous.” Danmaku turns raw panic into a dance — a pattern that looks unsurvivable resolves into one obvious gap you slide through at the last frame.

Pillars

Density that reads. Every pattern is a legible shape (spiral, aimed spread, wall-with-gap). Difficulty comes from tighter gaps and faster waves, never from noise. Density ≠ difficulty.
The gap is always there. Fairness is provable: a greedy lookahead dodger clears deathless. If the bot can’t survive, humans die unfairly — that’s a bug, not challenge.
Uptime is the game. Dodging is trivial; the skill is holding your fire lane on the boss while dodging. Reward aggression under pressure.

The loop stack

Scale	The beat
Moment	Read the next wave’s shape → slide into its gap → keep firing.
Encounter	A boss’s pattern sequence: phases escalate; each phase teaches its gap before it speeds up.
Session	A stage: trash waves as breathers, midboss, boss. Graze/point economy rewards flying close.
Meta	Score chase, unlock ships/patterns, difficulty tiers (easy = wider gaps, same shapes).

Essential systems

System	Why it’s load-bearing
`system-telegraphs`	Every pattern’s spawn point and direction must be readable before it’s lethal — the tell is the fairness.
`system-boss-design`	The boss IS the content; phases are the difficulty ramp. Spectacle + honest tells.
`system-grace`	Mercy clears on death and at phase transitions are structural — without them deaths cascade (FUN.md law 5).
`system-difficulty-and-dda`	Difficulty tiers = wider gaps / slower bullets on the same patterns, not new ones.
`pattern-readability`	Player bullets, enemy bullets, and the tiny hitbox must never blur together.

Content & difficulty model

Pattern library, not level data. Author reusable emitters (spiral, ring, aimed n-spread, wall-with-moving-gap) parameterised by rate/speed/count. Stages are sequences of patterns; difficulty is the parameters.
Ramp by geometry. Widen or narrow the gap chord; speed up bullets; overlap two patterns. Cap peak on-screen bullet count and assert it — a spike past the budget is a frame-rate cliff, not difficulty.
Breathers are structural. Trash waves and post-boss lulls let the player reset. A stage that never breathes reads as noise.
Verify the gap exists. The greedy dodge bot must clear every stage deathless before you tune numbers — see system-difficulty-and-dda and the verify link below.

Signature-mechanic seeds

Bullet hell but you place the bullets (mechanic-swap) — a reverse shmup: you author the enemy’s next pattern from a hand, then dodge your own design.
Bullet hell but time only moves when you do (constraint) — SuperHot for danmaku; density becomes a spatial puzzle instead of a reflex test.
Bullet hell but the gap is drawn in ink (theme + tonal) — a duotone ink-brush look; every wave is a brushstroke, grazing “wets” the paper for score.
Bullet hell but co-op share one hitbox (perspective) — two players, one ship’s life pool; threading requires reading each other. Pairs system-coop-and-competition.
Bullet hell but bullets are the platform (mechanic-swap) — stand on slow bullets to reach the boss; movement and dodging invert.

Pick one and let it ripple: a strong bullet-hell twist changes the scoring economy (what grazing means), the pattern authoring (who places the bullets), or the hitbox itself — not just the skin. See process-the-twist.

Common pitfalls

Noise mistaken for depth. More bullets ≠ harder; unreadable ≠ challenging. If a death feels random, the pattern didn’t telegraph.
No mercy on death. Reviving into a live pattern chains deaths — always clear the screen and grant i-frames (law 5).
Hitbox lies. If the visible sprite is the hitbox, players die to grazes that looked clear. Hitbox must be a tiny, honest sub-pixel.
Passive is optimal. If parking in a corner survives, uptime isn’t rewarded — pull the player forward with graze/point economy.
Difficulty tiers are new patterns. An “easy” mode that swaps in different shapes doubles your authoring and splits your proofs. Same patterns, wider gaps — one library, many tunings (system-difficulty-and-dda).

Anchors

anchor-nuclear-throne — arcade twin-stick reflex mastery; the tight run-based loop and readable enemy fire translate straight to danmaku.
genre-horde-survival — the sibling “rising tide” genre; borrow its density-that-reads discipline, swap auto-attack for manual dodge.

Verify

Prove it in FUN.md §7 · Bullet hell: the greedy lookahead dodge bot clears deathless, peak-bullet count is asserted, and the per-step time budget holds.

Composes with

system-telegraphs — the tell that makes a wall of bullets fair.
system-boss-design — the phased set-piece that is the whole encounter.
system-grace — mercy clears and i-frames as structure, not polish.