How to Unlock Koishi Boss Fight in Touhou Blooming Chaos 2

A guide on how to unlock Koishi as a boss fight in Touhou Blooming Chaos 2~! Koishi’s special, and she would like some items from you!


Welcome player! This is a brief guide on how to unlock Koishi as a boss fight in Touhou Blooming Chaos 2. There isn’t really a steam guide for Koishi’s fight for nearly 2 years since she got added, and I felt like this should be a nice guide someone can look at if they don’t know how to fight her (or doesn’t even know she’s in the game as a boss!)

It’s worth pointing out that you DON’T NEED DLC 2 to fight Koishi in this game. You can start Koishi’s boss fight the moment you discover her special room, and DLC 2 only provides Koishi as a playable character for you

How do we find Koishi?

First, we need to find Koishi’s room! Koishi’s room is a special room that may randomly spawn when you’re doing dungeons. Each dungeon has a various chance of spawning a special room, and the room CAN BE Koishi’s boss room, but it’s never guaranteed.

If you want to increase the special room spawn rate, you can equip “Ordinary Rabbit’s Skirt” (Tewi’s Dress Card) which increases the rate by 1~3% per card, and it stacks.
Example: You can equip 6 Phantasm “Ordinary Rabbit’s Skirt” to increase the special room spawn rate by ~18%.

Koishi’s Special Room

With enough dungeon runs and special room spawn rate, you will eventually find a special room with a purple telephone in the middle with music stopping and no ambiance when you enter.

You can now begin unlocking Koishi’s boss fight by simply getting close to the telephone and talking to Koishi with the “Dial any number”option.

Koishi wants—

This where a “quest line” for Koishi starts after you talk to her, requiring you to deliver a total of 10 consumable items before you can actually fight her.

She will request some random consumable items that you must deliver to continue. The items she wants are shown above the telephone, as seen below.


When you have the item, you will simply throw/drop the item on the ground and the telephone will “absorb” the item. You need to throw the item in front of the telephone so she can collect it.

After a few seconds when the item is “absorb”, you must talk again to Koishi to continue. She will thank you, and then reward you with a “Forbidden Number”. We’ll talk about the “Forbidden Numbers” in a bit.

When you talk to her again after giving you the “Forbidden Number”, she will simply thank you again and say it’s a good day.

This is basically it. You will repeat this 9 more times (total of 10), with the 11th encounter being the boss fight if you dial her. You don’t immediately fight her after you delivered the 10th item. Below are notes on about Koishi’s “quest line” that you may find useful:

  • After you deliver her an item she asked for, she will no longer ask another item on that floor, and as mentioned, will simply thank you again. This means you will need to encounter her again in a different floor before she ask for another item, which you can deliver immediately if you have it.
  • If you don’t have an item that Koishi request and you left the floor without it being delivered, Koishi will ask the same item on the next encounter. This allows you to take one from your storage (if you have one in it) or buy one from Kourindou in the human village before you go to another dungeon as a preparation.
  • Koishi’s special room will only spawn if the dungeon can spawn a special room. Dungeons like Boss rush, where every floor is a story-line boss, will not spawn Koishi’s special room even if she’s technically a boss.


Once you’ve finish her 10 item request, on the 11th encounter and onwards, you can trigger Koishi’s boss fight once per floor by dialing her again with the telephone on the middle.She’s an aggressive boss that has a lot of AoE’s and invincibility that makes her invulnerable to damage.

  • Recommend to pack a lot of healing potions, Shanghai Dolls and even MP potions for your abilities.
  • Koishi does not have a lot of health, but she gains invulnerability if you hit her too many times/deal too much damage in quick succession (shown by her having a clear bubble around her). If this happens, try to avoid her attacks when the invulnerability is up.
  • Koishi has a specific attack where she tries to attack from the back of your character. You can avoid this if you dash when the red dot becomes barely visible which instantly removes Koishi from you and prevents damage. However, if you missed it, you will be unable to attack or move and will take HUGE amounts of damage. Heal with a lot of pots so you don’t die.
  • When defeated, she has a chance to drop her dress card. The effect is every time you dash, your character releases an aura that deals damage to nearby opponents, much like her own dash during the boss fight.

“Random” Phone Numbers

Every time you give an item to Koishi, she rewards you with– “Forbidden Numbers”. These numbers just particularly lets you talk with some other touhou characters. You can see what numbers you’ve collected by using the telephone and clicking “Dial a number in the contact list”.

You can talk to them unlimited number of times, and purely just serves as an experience. You don’t even need to talk to any of them to fight Koishi.


Guide is quite simple and straight-forward to be honest. I decided to make this quite late since I actually stopped playing the game when cloudsave destroyed saves and was to lazy to start over since I had good amount of progress back then. The original save I had is on the youtube video above, which was way back– 2021….

Just picked the game back and noticed there isn’t really a guide for Koishi considering she’s actually the most problematic hidden boss to unlock. (Although to be fair, the other 2 isn’t that hard as well).

Hopefully, you found this guide helpful if you ever have problems unlocking her!

This guide about Touhou Blooming Chaos 2 was written by Misuki. You can visit the original publication from this link. If you have any concerns about this guide, please don't hesitate to reach us here.

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