Obtain ISO and patches for the game

https://www16.big.or.jp/~zun/html/th08dl.html

東方永夜抄　～ Imperishable Night.iso
md5 F0C8B50089ED55BC1BCF1BC3E9614A68

eiya_update100a.exe
md5 3269D49D81EAFAE366BD6B2AEA4AE82D

eiya_update100a_100d.exe
md5 CD70AE93BF282331DF22A3C3159B1429

Download and install Locale Emulator (or change your computer locale to Japan)

https://xupefei.github.io/Locale-Emulator/

Mount the iso file and run install.exe with Locale Emulator -> Run in Japanese (Admin)

(HIGHLY RECOMMENDED) Click 参照 button to change installation path (Yes the path appears with ¥ symbols instead of \ because of ancient computer limitations). Change to something like C:\Games\th08

click 開始 to begin installation click OK to confirm installation

---------------------------
確認
Confirmation
---------------------------
スタートメニューにショートカットを作成しますか？
Do you want to create a shortcut to the Start Menu?
---------------------------
Yes   No   
---------------------------

Select whatever (probably no as we will use different method for launching)

---------------------------
確認
Confirmation
---------------------------
デスクトップにショートカットを作成しますか？
Do you want to create a shortcut on your desktop?
---------------------------
Yes   No   
---------------------------

Select whatever (probably no as we will use different method for launching)

---------------------------
確認
---------------------------
インストールは成功しました
Installation was successful.
---------------------------
OK   
---------------------------

Install official patches

(HIGHLY RECOMMENDED) If you didn't change the installation folder name before, rename installation folder to only have English characters 東方永夜抄 -> th08
run eiya_update100a.exe with with Locale Emulator -> Run in Japanese (Admin)

---------------------------
東方永夜抄 アップデータ(1.00 → 1.00a)
Touhou Eiyashou updater (1.00 → 1.00a)
---------------------------
東方永夜抄 をバージョン 1.00 からバージョン 1.00a に更新します。
You are updating Touhou Eiyashou from version 1.00 to version 1.00a.

よろしければ「はい」をクリックしてください。
Please click “Yes” if you wish to do so.
---------------------------
Yes   No   
---------------------------

Click Yes and select 参照 ... your installation directory (default is C:\Program Files (x86)\東方永夜抄), click OK

正常にアップデートされたように見えた
Seemed to update normally.
---------------------------
閉じる(C)
Close (C)

Press 閉じる(C) and 閉じる(C) again.
Repeat the same steps for eiya_update100a_100d.exe (it updates a -> c, then c -> d)

Notes for Nvidia

If you are using Nvidia GPU, open Nvidia Control Panel, navigate to Display -> Adjust desktop size and position and make sure that scaling mode is set to Aspect Ratio and Perform scaling on: GPU is selected. Else game will be stretched or crash on launch.

Fixing input lag

https://www.reddit.com/r/touhou/comments/1fdd3z6/psa_how_to_actually_fix_input_lag_especially_in/
Download latest stable dgVoodoo2
https://dege.freeweb.hu/dgVoodoo2/dgVoodoo2/
copy over dgVoodoo.conf, dgVoodooCpl.exe and MS -> x86 -> D3D8.dll
launch dgVoodooCpl.exe
General tab:
Scaling Mode - Stretched, keep aspect ratio
DirectX tab:
uncheck - dgVoodoo Watermark

Right click dgVoodoo banner on top click Show all sections of the configuration

GeneralExt:
Presentation model - Flip discard
Apply and close dgVoodoo2
Install Special K
https://discourse.differentk.fyi/t/download-special-k/1461, download archive, open archive and copy SpecialK32.dll to your game installation directory rename file to d3d11.dll
launch the game

⚠ If the game crashes on startup, close MSI Aferburner and RTSS also try setting game to Windowed in dgVoodoo2 General tab and pressing alt+enter when game loads

now you should see special k notice pop up, open the menu with ctrl+shift+backspace
Go to Framerate Limiter right click on 60.000 fps toggle on Latent Sync, Delay Bias select 90% input, 10% display, if it lags select lower input value, go to NVIDIA Latency Managment and change Reflex mode to Low Latency
On Screen Display (OSD) - Disable Show Startup Banner

English Patch

Download thcrap https://www.thpatch.net/wiki/Touhou_Patch_Center:Download extract files somewhere that you won't delete, run thcrap, select your language, Find Games select Find games in a specific folder... select your installation directory, tick both items, select where to create shortcuts