A short guide to the Krkr2/KrkrZ ecosystem for the western reverser/translator/developer.
Wherever the document names the author of a system, you should mentally append (and contributors).
Comments and pull requests welcome.

Disclaimer

This document effortlessly mixes my own conjecture and estimates with actual documented fact.
Don't take any of this as holy scripture. This is just a starting point. Let me know where I'm wrong.

How to edit Shift-JIS and UCS-2 encoded script without JP system locale

Use Sublime Text with the ConvertToUTF8 plugin.
Despite its name, this plugin actually also adds transparent support for SJIS text encoding, which Sublime Text lacks natively.

Systems

KRKR2 / KiriKiri2

KRKR2 aka KiriKiri2 is a game engine that executes its own TJS script language, somewhat similar to JavaScript.
It was created and developed by W.Dee as a rewrite of their original KiriKiri engine.
KRKR2 has been thoroughly outdated for well over a decade, and is generally not used by new projects.

• KRKR2 Source tree: https://github.com/krkrz/krkr2/tree/master/kirikiri2/trunk (Time-frozen/Read-only copy)

KRKRZ / KiriKiriZ

KRKRZ however is a more modern fork of KRKR2 and is still widely used and supported.
KRKRZ features a separate backwards compatibility layer for Krkr2 scripts called k2compat.
This document in general will refer and link to KRKRZ versions of plugins etc, where available.

• KRKRZ Source tree: https://github.com/krkrz/krkrz
• KRKRZ Docs: http://krkrz.github.io/documents/

K2Compat

A backwards compatibility layer to allow KRKR2 scripts to run under KRKRZ.

• K2Compat Source tree: https://github.com/krkrz/Krkr2Compat

KAG3

KAG3 or "Kirikiri Adventure Game" is a scene and UI building system written by W.Dee in TJS for KRKR2/KRKRZ.
KAG3 runs .ks files and is the base system on top of which almost all KiriKiri VNs are built.

• KAG3 Docs: http://kirikirikag.sourceforge.net/contents/index.html
• KAG3 Source for KrkrZ: https://github.com/krkrz/kag3

KAGEX

KAGEX is an extension of KAG3 by wtnbgo/Watanabe Go.
Some other extensions exist for KAG3 which are incompatible/mutually exclusive with KAGEX, but in practice
KAGEX is by far the most common choice for developers. You can tell whether a game uses KAGEX by the
existence of a plugin called KAGParserEx.dll or multiple system scripts named KAGEnv*.tjs.
KAGEX has been documented quite extensively by sakano/Naoya Komatsu.

• KAGEX3 Source tree: https://github.com/krkrz/krkr2/tree/master/kirikiri2/branches/kag3ex3 (Frozen copy)
• KAGEX3 Class diagram: http://blog-imgs-43.fc2.com/k/a/s/kasekey/kag3ex3_class.png
• KAGEX Docs: https://biscrat.com/krkr/docs/kagex/contents/
• KAGEX Book: https://github.com/sakano/krkr_archives/raw/master/doc/kagex_book/KagexBook.pdf
• Sakano's blog/articles on KAGEX and related usage: https://biscrat.com/blog/kagex-articles/

Glossary

• TJS: The script language executed by the KiriKiri engines. Similar to JavaScript, but unique.
  File extension is .tjs, but the file itself can be either a plaintext script that is compiled on the fly by the engine,
  or it can be a precompiled binary file which contains just the assembled TJS virtual machine instructions.
  Apart from basic string replacements, there are no reliable or convenient ways to edit compiled TJS script.
  Disassemblers let you see what the TJS script does, but the disassembly cannot be parsed back into runnable TJS.
  A decompiler can be found within the Furikiri project and run from the command line via its Girigiri interface,
  but this only works for relatively simple and short TJS files. The success rate for decompilation of TJS files found
  in the wild is in my experience about 20%. If you need to modify a precompiled TJS script (other than the string replacement,
  which can be done with ScnEditorGUI) and the decompiler fails, generally you're SOL.
  Thankfully, however, most TJS that ships with games is actually unmodified open source and can be found online.
  sakano has written a TJS syntax highlight for Visual Studio Code, available here.
• KAG: The visual novel/adventure game system that takes care of basic UI and UX, layered rendering and
  game state machinery for the game developer's convenience. KAG is written entirely in TJS, and is itself
  a processor for KS (KAG Script) files. KAG Script is a simple tag-based language, and a whole game can be
  written in KS alone. Often, however, developers will use additional systems for ease development on top of KAG,
  which relegates the KS scripts to mostly serve the menu and UI role.
  One such example is the commercial? SCN scene format and parser by M2 Co. Ltd.
• KS: KAG Script file format. Very simple text-based script that uses a tag system and rudimentary
  assignment and comparison operators to create interactivity. Usually a game's menu, config and staff roll
  at least are written in KS. However older and smaller VNs in particular can also be written entirely in KS.
• AMV: A custom video file format which features an alpha channel, implemented by plugin AlphaMovie.dll.
• SCN: TLDW
• PSB: TLDW
• TLG: Image file format used for foreground sprites, i.e. character art.
  Convertible to and from PNG by tools like GARbro and the FreeMote PSB Toolkit.
• SINFO: A tabulated text file that maps names for characters' attire, expressions etc. to the corresponding images.
• SOL: Shit Outta Luck

Dialogue in KAG/KAGEX

Games built on the KAG system have multiple different methods of implementing their dialogue parsing.
I'll probably document the actual possible sources of the dialogue sometime later;
For now I'm just adding a word about text formatting.

Fonts and default formatting

For many VNs their dialogue stays visually rather static throughout, and might be monospaced.
Monospacing is natural for Japanese kana & kanji, but should have no place in western dialogue text.

In fact, shipping a game with monospaced dialogue in English ought to be outlawed.

Default text formatting is usually set in default.tjs, so look there first and see if your issues can be solved
by a simple font change. A list of embedded font files to load is usually defined in embfontlist.tjs.
The available font names used to refer to faces within scripts, then, are the Dictionary keys from that file.

You'll figure it out.

In-line commands and effects

As for in-line effects like colors, alignment, speed changes, awaits and so on, there are a couple ways
a KAG-based game might parse them. The first is textrender.dll. This DLL exposes a TJS class called
TextRenderBase, on top of which a corresponding textrender.tjs implements a proxy class called TextRender.
I've documented the syntax for TextRender-based text formatting in a sister repository.

A script-only version of textrender.tjs which does not utilize the DLL also exists and ships with some games.

The other possibility is texttagconverter.tjs. This script processes a syntax similar to that of TextRender
into KAG script tags before the text is fed into the KAG parser. I might document this later.

A third possibility is that the dialogue is written directly in .ks scripts, and can therefore use
the KAG tags to achieve effects as usual. This was how things originally worked, but no recent or even
semi-recent VN puts dialogue directly into .ks scripts. I'll write more about this at some point.

Automatic word-wrapping implementations are usually tacked onto these scripts, if used.
The original Japanese script files do not do automatic word-wrapping.

Plugins

A major part of the KiriKiri engines' success is their extremely comprehensive support for plug-in DLLs.
A massive number of plugins exist for the engine(s), and are used to implement anything from clipboard support to additional renderers, custom audio mixing and interactive catgirls. This is a sorely lacking list of some plugins by their filename, for which I've been able (and cared enough) to identify a source.

• AlphaMovie.dll: Free but not open source. Implements movie files which have an alpha channel.
  These files have the .amv extension. Encoder and playback via http://kaede-software.com/krlm/plugin/alphamovie.zip,
  Decoding/dumping via https://github.com/xmoeproject/AlphaMovieDecoder
• extNagano.dll: Free but not open source. It is used to implement numerous layer transition effects.
  Used to be available at http://ymtkyk.sakura.ne.jp/krkr.STG/plugin/extNagano.html, but I haven't found a copy of the archive.
• extrans.dll
• getSample.dll: Used for reading sample data from WaveSoundBuffer, usually for mouth movement.
• k2compat.dll
• kagexopt.dll
• KAGParser.dll: This is the core parser module of KAG3.
• KAGParserEx.dll: This is the core parser module for KAGEX3. It replaces KAGParser.dll when using KAGEX3.
• krmovie.dll
• layerExDraw.dll: Implements support for drawing onto Layers with GDI+.
• lzfs.dll: KiriKiri LZ4fs Plugin. No source found.
• menu.dll: Implements Window.menu to enable Win32 window menu bars.
• PackinOne.dll
• pkutil.dll: Provides public key cryptography utilities, generally used to verify file signatures and/or product keys.
• psbfile.dll: TLDW
• psd.dll: Possibly https://github.com/wtnbgo/psdfile
• textrender.dll: A native code replacement for the all-script TextRender.tjs from KAGEX3. Source unknown.
• win32dialog.dll: For displaying native Win32 dialog boxes.
• win32ole.dll: Allows calling into Win32 OLE/ActiveX components.
• windowEx.dll: Extends the TJS Window class with some events and multi-monitor stuff.
  Mostly used to implement window resizing with a fixed 16:9 aspect ratio.
• wuopus.dll: Adds support for Opus audio file playback.
• wuvorbis.dll: Adds support for Ogg/Vorbis audio file playback.