[PC-98] How an obscure fighting game for Japanese PCs can ruin your day

This is a guest post from spaztron64

Sometime in June 2023, I came across a Twitter post by kuma_neko24 where he detailed his struggles in getting Policenauts to work on his PC-9821 V166. As I own the exact same machine, I figured I should give it a shot myself and report the results.
Unfortunately, while I was experimenting, I had hit a strange situation where certain executable files would randomly corrupt themselves and become unusable:

I figured the game might’ve been the culprit, but after restoring the most recent backup, the same thing happened not long after, without even trying to play the game. I’ve done Memtests of the SDRAM, as well as block level diagnosis of the CF card, and they were fine, so I attributed it to a corrupt filesystem.

I then restored a much older backup, and moved over all the known good files from the recent backup. Things seemed fine for a while, but then the exact same situation happened again. I decided to look into the issue in more detail, and I’ve noticed that affected files like WIN.COM and KRNL386.EXE were 3KB larger…. as we’ll see later, this should’ve been an immediate red flag, but I yet again brushed it off as a bad filesystem or CF card.

Fast forward to March 2024, and I got myself a set of new CompactFlash cards. I had once again restored the last known good backup, and for about a day everything seemed alright, until….

Needless to say, all my previous hypotheses turned out to be wrong. As such, I investigated yet again into the corrupted files, and used windiff to take a closer look into what actually changed. Let’s take a look at WIN.COM, SCANREG.EXE and KRNL386.EXE:

We can observe the following pattern:

  1. The files always grow in size
  2. windiff shows that the header is modified and that a bunch of garbage is added at EOF
  3. It’s always the same exact garbage
  4. Additional examinations show that MEM.EXE also has these modifications
  5. MZ headers are present, so it’s certainly executable code

By every metric, this isn’t a set of accidental corruptions, these are deliberate infections.

I then proceeded to take a sample of the suspiciously added code, did a byte scan of every file on the card, and isolated the following programs as infected:

  • B:\WIN31\WIN.COM
  • B:\SBVGM\VGMPlay.exe

Most of these are self-explanatory, apart from the last two.
VGMPlay is a program by Scali that allows playback of OPN(A) and OPL3 VGM files even on PC-98s without a SoundBlaster 16/98. I know this program is not the culprit, since the original program I got is clean.
DGP, on the other hand, is a different story, and it needs a bit of a foreword.

Duelists and queens!

DGP is a shorthand for “Duelist Gaiden Plus”, which refers to the game “Queen of Duelist Gaiden Alpha Plus”.

The original Queen of Duelist is a rubbish game not worth anybody’s time or any further mentions.
Queen of Duelist Gaiden Alpha is the 1994 sequel, which is a significantly better game, and arguably one of the best fighters for any personal computer at the time, featuring:

  • 10 fully voiced characters
  • Adjustable game speed
  • Dual PWM sampling over the integrated PC beeper speaker
  • Decent performance on a 286, and more

At the end of 1994, Agumix released an upgrade for the game called “Queen of Duelist Gaiden Alpha+”, which introduces some quality of life improvements. This update requires the original Gaiden Alpha to already be installed, although it doesn’t do any differential patching, it just replaces existing files with newer variants, and adds the DGP.EXE executable to be used instead of DGA.EXE. Shockingly, all of my older backups containing the patch, as well as the dump of the disk itself (available on Neo Kobe PC-9801) contain the suspicious code.

I didn’t expect it to return any results at first, but I uploaded DGP.EXE to VirusTotal for scanning, and well…

Who would’ve thought, the update was distributed with a copy of the Yankee Doodle virus embedded within!

Yankee Doodle is a very simple COM and EXE self-injecting virus from 1989. When executed, it resides in memory and infects COM and EXE files that use certain INT 21h DOS API calls, which include the files in the above list. It’s payload is normally supposed to play the Yankee Doodle tune through the PC speaker at 17h every day, but on PC-98 what it does instead is catastrophically fail and crash the entire system. It’s infection routines, however, do work.

A thing worth pointing out is that the infection routine is not automated. It will only engage when executing other programs from DOS manually. This should never be possible after starting the game, since there’s no way to return to the DOS command line without a full system reboot…

… unless you tried to start the game with not enough free memory, after which the game will dump you back to DOS. Pretty much every DOS user would, in situations like this, start MEM (preferrably with the /C and /P flags) to check what uses so much memory and how little remains free.

Sadly, for us, Yankee Doodle remains memory resident in this case, and it infects MEM as soon as it’s run, which explains how it got infected. Now every time you check your memory, the virus will be waiting to spread further.

Well, now what?

No known clean copy of the Plus version is known to be in circulation, and the only available source currently is the compromised disk image on Neo Kobe.
Additionally, nobody knows if the game was originally distributed with the infection, or if the person sharing a dump of the game around through P2P back in the 1990s had infected his copy.
As such, unless an original physical copy is found on auction, dumped, and confirmed clean, the only solution is to patch out the infectious payload from the game. Until then, do not play Queen of Duelist Gaiden Alpha Plus on your PC-98 machine!

EDIT 2024-03-31:
Fortunately it appears that the “Alt 1” dump available on Neo Kobe has a clean copy of DGP.EXE.
DrNyquist has also confirmed that this torrent also has a clean dump.

Conclusion: steer clear of the primary dump on Neo Kobe, use the others mentioned above.

Are you Japanese?

On my latest trip, I managed to find a copy of Zork 1 for the PC-98! And let me say, let the adventure begin!

I went to Beep and the place next door I always forget it’s name, and I found this burried in the back for a mere Â¥2,860! Not exactly what I thought would be a bargain, but flipping it over however…

Zork 1 for the PC-98!

Â¥7,800 YEN! From 1991!Honestly I don’t even know what is up with the price of software in Japan! Clutching this thing in my hands for the Â¥2,800 makes it feel like a steal so of course I buy it!

Contents of the box

Nice to see that opening of the box gives me a catalogue, a manual, minimal map, registration card and a diskette! And I’m hoping I can read it using a USB drive.

Now I have no pc98 gear in Japan, and I’m trying to not have a mountain of hardware here, the i7 desktop and 30″ cinema display are already feeling ‘too big’ for this place anyways. I go to hardoff and pick up 2 USB floppy drives hoping to read the 3 1/2″ diskette.

Now I bought an IBM & some weird iMac looking drive, I was hoping between the two drives, maybe one would work. And I was right for buying the two. The IBM drive didn’t read the disk AT ALL.

However this iMac looking Logitec LFD-31US did the trick!

Apparently you need what is known as a “3-mode USB floppy drive”. Whatever that means. Although I can read the disk fine from Windows 10, winimage was unable to make a disk image. Disk Explorer is another option, which also specializes in the PC-98’s weird 1.2MB on a 1.44MB disk, however it couldn’t read the disk either.

I write a simple C program to read 512, 1024, 2048 blocks from \\.\A: (the physical drive), however it was cut short after 138kb. Maybe a hidden bad sector? Xcopy ran without issues, so who knows.

Looking at what I could dump, it does look like a bootable image:

and the xcopy did pick up MSDOS.SYS & IO.SYS. I though Microsoft was so against people redistributing MS-DOS, but then again aren’t most PC98’s floppy only?

I was able to cobble together a DIY disk image, and it doesn’t work fully on Neko Project II sadly. However Annex86 works fine.

On boot there is a nice graphical logo, and animation as the door opens. Really cool I have to say. Searching through zork.exe there is some interesting strings

  • Are you Japanese?
  • MS Run-Time Library – Copyright (c) 1988, Microsoft Corp
  • Original copyright (c)1988 Infocom Inc.
  • Used under license from Activision. All rights reserved.
  • (c)1991 SystemSoft
  • Copyright VACS Corp./ASCII Corp.,1986-90.
  • @(#)sunedit.c 1.0 07/03/1989 by VACS Corp.

Well that’s interesting. I was wondering how to trigger the ‘Are you Japanese?’ and well it turns out it’s pretty simple:

I’d have to figure out how to type in things like eat/sleep take… Although it is a twist on the old Infocom style. Now could this have ‘saved’ Infocom before their sale to Activision? I guess there was a market for Infocom games in Japan, although probably far earlier than 1991.

DooM 1.2j1.0 on NekoProject II

So the first thing you’ll need is Neko Project II.  It can be a little hard to track down downloads, but there is a whole slew of them here:

http://ux.getuploader.com/emu/index/1/date/desc the site has since moved to here:


https://simk98.github.io/np21w/download.html (it moved again)

So for now this link, is the latest build, which was last updated on

Extract that, and rn np21nt.exe

You’ll want to configure the sound.

MIDI options

MIDI options

If you choose to use the MIDI you’ll have to map them to a MIDI-OUT port, and I used the default Microsoft GS Wavetable.  Of course you could use MUNT, or any other MIDI mapper or port.  Also you may want to setup the serial port MIDI as a backup plan.

Serial MIDI

Serial MIDI

The sound effect settings work best for the PC-9801-86 audio board.


Select the correct board!

I’ll save installing MS-DOS, and installing DooM for another fun episode, but to configure DooM.

Run setup.exe to setup DooM!

Setup menu

Setup menu

The menu is simply:

  • 1 graphics
  • 2 Background Music
  • 3 sound effects
  • 4 not sure
  • 5 controller



The PC9821A driver works best from what I’ve done in my limited testing.  I guess if you had a different emulator, or a real PC-98 you’ll get more out of this.

Next is the BGM or music



You really have 2 options here, #3 for the PC9801 driver which uses the YM2608 chip.  Or the General MIDI either option 4 or 6. I didn’t notice any difference between the two of them, they both sound kinda slow, but workable.

Now for the audio board, select the PC-98

Doom sound drivers

Doom sound drivers

The PC-9801-86 is what you want here.  Now with either a 100% PC-9801-86 config, or a 50/50 of the MIDI/PC-9801-86 we are ready to run DooM!  Selection option 6 and away we go!

Save settings and run DooM

Save settings and run DooM

And all being well you’ll get the start of DooM!

DooM starting up

DooM starting up

Otherwise you’ll get this fun error:

DX386 error

DX386 error

In this case I had emm386.sys in my config.sys which conflicts with the dos extender DX386.

Personally I find it easier to boot off the #1 install diskette which will automatically start DooM!

If you are feeling brave, listen!

Qemu & the PC98

I have only seen one NEC PC-98 in my life, and naturally it was in Japan.. Wiki has a great article, (naturally), basically it was an intel powered IBM incompatible system, that ran an adapted version of MS-DOS localized to Japanese. It wasn’t until the introduction of Windows 95, did these machines die out, as 95 could be localized pretty well..

Anyways, after googling around to see who linked my builds of Qemu, I found this site, by Takeda Toshiya that includes patches and binaries for PC-98 emulation via Qemu!

I understand the PC-98 had quite a following for all kinds of games as people shifted away from the Sharp X68000.. Who also announced last week that they would exit the PC market all together.