This is a guide on how to use pjsekai-overlay-english, an English TL of pjsekai-overlay. This also includes how to navigate AviUtl, but only the bare minimum required for this purpose. This guide assumes you're using the latest pjsekai-overlay-english version, unless stated otherwise.

DISCLAIMER!!

I do NOT speak Japanese. I figured out everything by trial and error. Some parts of this guide may be partially or completely wrong.
Nanashi. (author of pjsekai-overlay) have stated time and time again that they WILL NOT help English users. This and AviUtl are tools intended for Japanese-speaking people. If problem arises, DO NOT ask Nanashi. for help. Instead, DM me on Discord (@khronophobia). (Opening an issue or discussion here is an option, but I'm more likely to notice if you DM me.) Sorry, but I don't feel like supporting people with this anymore. If you need help, you have to ask someone other than me, or you're on your own. I hope you understand.

Prerequisites

Make sure to have the following before following this guide.

1. A 720p mp4 recording of a Chart Cyanvas/Potato Leaves chart with Hide UI enabled
2. Basic knowledge of video editors (not necessarily AviUtl)
3. Basic knowledge of how to use a PC
4. Reading comprehension
5. Common sense
6. Determination to follow this to the end

I won't help you on obtaining all of the above. You're on your own for this one.

Instructions

Part 1: Installation

1. Download AviUtl v1.10 and extract it somewhere

2. Download easymp4 and extract it to plugins (Create the folder if it's not available)

3. Go here to download L-SMASH-Works. Download the one that ends with Mr-Ojii_Mr-Ojii and extract it to plugins

4. Download AviUtlEnMod-1.1.0.zip from here. Extract aviutl.ini to the base AviUtl directory, and the rest to plugins

5. Download Unmult.zip from here.

6. Inside plugins, create a folder named script (if not already available) and extract unmult.anm and Unmult.dll inside

7. Your AviUtl folder should look like this:
   Base folder
   
   Plugins folder
   

8. Go to the Releases page and download pjsekai-overlay-english.zip. Extract it anywhere

Part 2: Setting Up a Project

1. Make sure that AviUtl is still open, then launch pjsekai-overlay. Follow the instructions there. Once you see Execution complete, you're good to go
   
   (If your pjsekai-overlay is in Japanese, go back to Step 8 of Part 1 to download my fork)

2. Restart AviUtl

3. If the Advanced Editing window isn't already open, hover over Settings and click on Advanced Editing...
   

4. On the Advanced Editing window, right click on the timeline and click Create a New Project. Set the image size to 1280x720 and the frame rate to 60.

5. Right click on the timeline again and on File, click on Import object file
   

6. A file explorer window should pop up. Navigate to your pjsekai-overlay directory, and then dist/[chart id] and select main.exo

Part 3: Editing

This is where the fun part starts. Refer to AviUtl Reference if you ever get confused. If you have experience with video editors of any kind, this section should be significantly easier.

Something like this should pop up after you imported main.exo.

Double click on video file and change Reference file to the video you recorded. Set 'X' to '0' and 'Zoom%' to '100'.

Depending on the chart, the video and UI might stop early or keep going even if the chart already ended. If this is the case, resize the objects highlighted in red and drag the objects highlighted in green until it matches the end of the video. Be sure to drag the end keyframe (blue arrow) on the video as well.

Make any modifications as needed. Once everything is satisfactory, move on to Part 4.

Part 4: Exporting

1. To ensure that the exported video doesn't end too short or goes on for too long, right click on the timeline and set the video end to the furthest object

2. Click on File in the AviUtl window and select either Export with AVI, or hover over Export with Plugins (recommended) and click かんたんMP4出力. Everything from then on should (hopefully) be straightforward.