Attack on R-Cyclone is the 1st stage of Crimson Catastrophe. Next stage: Wrath of R-Cyclone.
Red Cyclone has 999,999 HP and hits for 92,000 at 552,000 damage per second, so nothing you own survives one of its swings, however tanky. Its weakness is its reach: only 90. It doesn't appear until you hit the base, and it brings One Horns, which have even less reach and stand in front of it. This stage isn't about health. It's about keeping Red Cyclone from moving, and that job belongs to the crowd-control Rares from the Rare Cat Capsule.
The lineup that does it
Meatshields: Macho Cat, Samba Cat, Wall Cat and Brah Cats. UFO Cat clears the peons. Crazed Bahamut is the damage that matters. Then the crowd-control Rares. Red Cyclone is Red and Floating, so several work: Bishop Cat (Slow vs Floating), Witch Cat (Slow vs Red) and Shaman Cat (Freeze vs Floating) hold it still. Pirate Cat (Knockback vs Red) and Fortune Teller Cat (Knockback vs Floating) push it back, which is less reliable, as the next sections explain. If you've True Formed Bishop into Sanzo Cat, the stage gets much easier. Those Rares don't need levels: their damage barely matters and their proc chance doesn't grow with level, so keep your XP for other units, apart from level 10 for any Cat Combo they're part of. Kung Fu Cat and UFO Cat are expensive and unreliable here. Paris Cat or Drama Cats are better picks for your area damage if you have them.
Treasures and items
Every Empire of Cats treasure is required. Bring Rich Cat and Sniper the Cat if you can. The stage is doable without them, as the second run in the video shows, but it's more forgiving with them. Switch Sniper off once the One Horns are out, because its knockback makes Crazed Bahamut miss.
Before the base: clear the peons
Red Cyclone only comes out when you hit the base, so use the time. A Wall Cat stalls, UFO Cat clears the small fry, and Crazed Bahamut goes out the moment the five Shy Boys arrive. After he's cleared them, send only walls, crowd control and area damage. Everything else just fills the unit cap, and a full cap means no more walls when you need them. Kill St. Pigge the 2nd before you use the cat cannon.
UFO Cat on the peons, before the base is touched · plays here, from that second
Hold it, and kill the One Horns first
Once the base is hit, Red Cyclone comes out and gets Slowed straight away. From then on, keep meatshields, crowd control and attackers going out without a gap. The fight is really decided by the One Horns. They stand in front of Red Cyclone, and they're what your crowd-control units hit instead of it. Kill them first. That's Crazed Bahamut's job, and it only works if he isn't at the very front: from there he can't hit the One Horns. If he misses them, your front line goes. Use at least two crowd-control units, so one missed proc doesn't end the run.
Red Cyclone Slowed as soon as it comes out · plays here, from that second
Slow and Freeze beat Knockback
The type of crowd control matters as much as the number. Knockback looks strong but works against you here. While Red Cyclone is flying back, it can't be hit, so your attacks miss. And your faster units keep walking forward, into its range, and die. The video shows the full Captain Cat run to prove it, and it's close. Slow and Freeze keep Red Cyclone still, so every attack lands. If your crowd-control units stop proccing, the front line eventually breaks. That's why the second unit matters.
Knockback: attacks going into empty air · plays here, from that second
Without Rich Cat and Sniper
It works with no items too: the same walls, UFO Cat, Crazed Bahamut, True Valkyrie, Miss MONEKO, and Bishop, Pirate and Fortune Teller Cat all at level 1. Three crowd-control units cover for missing items: one Slow, two Knockback. If you have no Rare crowd-control units at all, a no-gacha clear is possible but much harder, and it can need a continue. Build your crowd control from the Rare Cat Capsule first.
the no-item run on the base · plays here, from that second
THE SHORT VERSIONClear the peons and the Shy Boys before you hit the base, then hold Red Cyclone with at least two crowd-control Rares (Slow or Freeze over Knockback) behind nonstop meatshields, and kill the One Horns first with a Crazed Bahamut that isn't at the very front. Levels on the crowd-control Rares don't matter.
The general approach, from the wiki's strategy notes. The guide above walks through one full clear.
Red Cyclone's damage per hit and DPS are so high that resistant units do nothing — even the toughest tank is wasted money. This stage is about crowd control, not health.
- Halt its advance with anti-Red / anti-Floating crowd-controllers: Witch Cat, Bishop Cat (whose True Form makes the stage trivial), Pirate Cat, Fortune Teller, Shaman, Delinquent or Apple Cat.
- Ubers and collab cats that affect Red or Floating (Momotaro, for one) do the same job.
- Add extra-damage cats where you have them so the peons and the Cyclone die faster once they are locked down.
FORTUNE TELLER CAT B Cats that work well are Witch Cat, Bishop Cat (whose True Form makes this stage trivial), Pirate Cat, Fortune Teller Cat, Shaman Cat, Delinquent Cat or Apple Cat, as well as some Ubers and collab cats that affect Red and/or Floating (like Momotaro). 
DELINQUENT CAT B Cats that work well are Witch Cat, Bishop Cat (whose True Form makes this stage trivial), Pirate Cat, Fortune Teller Cat, Shaman Cat, Delinquent Cat or Apple Cat, as well as some Ubers and collab cats that affect Red and/or Floating (like Momotaro). 
SHAMAN CAT B Cats that work well are Witch Cat, Bishop Cat (whose True Form makes this stage trivial), Pirate Cat, Fortune Teller Cat, Shaman Cat, Delinquent Cat or Apple Cat, as well as some Ubers and collab cats that affect Red and/or Floating (like Momotaro). 
WITCH CAT B Cats that work well are Witch Cat, Bishop Cat (whose True Form makes this stage trivial), Pirate Cat, Fortune Teller Cat, Shaman Cat, Delinquent Cat or Apple Cat, as well as some Ubers and collab cats that affect Red and/or Floating (like Momotaro). 
APPLE CAT B Cats that work well are Witch Cat, Bishop Cat (whose True Form makes this stage trivial), Pirate Cat, Fortune Teller Cat, Shaman Cat, Delinquent Cat or Apple Cat, as well as some Ubers and collab cats that affect Red and/or Floating (like Momotaro). 
MOMOTARO A Cats that work well are Witch Cat, Bishop Cat (whose True Form makes this stage trivial), Pirate Cat, Fortune Teller Cat, Shaman Cat, Delinquent Cat or Apple Cat, as well as some Ubers and collab cats that affect Red and/or Floating (like Momotaro). ⚙ Trait counters worked out from the roster — the guide's plan doesn't need them; kept for reference
Red Cyclone is Red. Anti-Red units take less damage and deal more.
FISH CAT A Strong Against Red and tanky for the cost — a sturdy anti-Red frontliner. 
ZOMBIE CAT B Strong against Red — 1.5x damage, takes 1/2. Also fits “Clear the crowd.” 
CARPENTER CAT A Resistant to Red — durable against Red attackers. Also fits “Counter Floating.” 
BATH CAT A Deals Massive Damage to Red enemies. Also fits “Out-range Red Cyclone.” 
CAT CLAN HEROES S Weakens and damages Red. Also fits “Out-range Red Cyclone.” Red Cyclone is Floating. Anti-Floating units take less damage and deal more.
SABER THE CAT C Saber Alter Cat: Strong against Floating enemies (Deals 1.5x damage, only takes 1/2 damage) 
ARCHER CAT A Deals Massive Damage to Floating enemies. Also fits “Out-range Red Cyclone.” 
BODHISATTVA CAT A Slows and (True) Weakens Floating enemies. Also fits “Clear the crowd.” 
CATMAN S Massive Damage vs Floating (Normal). Also fits “Out-range Red Cyclone.” 
HIGH LORD BABEL S Equally tough against Floating enemies, with Colossus Slayer. Also fits “Counter Red.” Red Cyclone reaches 90 range. Units that out-range it can chip safely without taking hits.
GROSS CAT A Range 350 — fires from beyond its 90. 
MASTER URIL A Range 405 — fires from beyond its 90. Also fits “Clear the crowd.” 
SALON CAT S Range 350 — fires from beyond its 90. Also fits “Clear the crowd.” 
CATWAY A Range 355 — fires from beyond its 90. Also fits “Counter Red.” 
MIGHTY REKON KORPS S Range 470 — fires from beyond its 90. Also fits “Burst the boss down.” Red Cyclone has a deep HP pool (999,999+ even before stage magnification). Heavy single-target burst shortens the fight.
BAHAMUT CAT S Huge multi-hit burst — a story-unlock powerhouse that deletes tanky enemies. MIGHTY REKON KORPS S Among the highest single-hit Area damage available. Also fits “Out-range Red Cyclone.” 
GAIA THE CREATOR S Long-Distance multi-hit with Insane Damage — a generalist wall-cracker. Also fits “Out-range Red Cyclone.” 
CRAZED MONEKO A Big crit burst against tanky/Metal targets. 
CHILD OF DESTINY PHONO S Big Multi-Hit Massive-Damage bursts from safety. Also fits “Out-range Red Cyclone.” 7 enemy types stack up here. Area attackers hit the whole push at once instead of one unit at a time.
URURUN WOLF A Area attacks hit everything in range. Also fits “Out-range Red Cyclone.” 
COURIER CAT A Area attacks hit everything in range. Also fits “Counter Red.” 
DELINQUENT CAT A Area Multi-Hit clears grouped enemies. Also fits “Counter Floating.” CATMAN S Long-range Area damage clears groups. Also fits “Counter Floating.” 
ACTRESS CAT B Hits multiple enemies at once for budget crowd damage. Also fits “Out-range Red Cyclone.” 
The castle you destroy to clear the stage.