OK, so before we even begin, a massive thank you to Youloute who provided so many corrections/gap filling/extra stuff, including translations from the Retro Game Test videos, made by people who emailed Nazca staff- those videos are here (In the Hunt & Gunforce II) and here (Metal Slug)- that their contributions are in itallics. Additionally, reader Kino was very helpful in pointing out some omissions in my list and where some of the staff members would end up afterwards, as well as the lone photo of the Nazca team .

So, to the point, Nazca is an odd company. Formed by Irem staffers in 1994, 2 months after Irem's arcade division closed, they started as a subsidiary of SNK, working on thier own, and were tasked with making games for the Playstation 1 and Saturn. During this time, Nazca began to work on Metal Slug for SNK's Neo-Geo, with a playtest version debuting in Osaka in August 1995 (more on that later). They also, of course, worked on Neo Turf Masters, but these are the only two games to carry the Nazca name, as afterwards they were moved to SNK studios but stuck together, unlike other parts of SNk which were divided into branches for sound, graphics and so forth.

Where it gets confusing, however, is what exactly did the members of Nazca get up to while they were at Irem?

This isn't a question with an easy answer. The credits for several Irem games are hidden in the high score tables rather than traditional staff rolls (if they even have them) and former members of Nazca are particularly tight-lipped- there's an interview translated from a Japanese publication with Kazuma Kujo (his first job at Irem was playtesting R-Type II, but he only ever worked on the first Metal Slug, and worked under the names Kire-Nag and Tobi_Nag) printed in Retro Gamer Issue 98 in which he says that team members like Akio, Susumu and Meeher worked on Gufnroce II / Geostorm, but can't divulge their real identities. Pseudonyms were common back then (and earlier- see also: The Fairyland Story) to prevent rival game companies from head-hunting, but this makes it a nightmare trying to figure out who made what. It's become a little easier in recent years with former members being more willing to talk for books like Metal Slug: The Ultimate History which is currently sat on my bedside cabinet, waiting for me to read it and extract all the necessary information from it, but I digress.

So. What we have is a smattering of Irem games that I checked for involvement from members of Nazca... Well, unless the sole Nazca member is Hiyamuta (HIYA!) as he did a lot of work witihn Irem before leaving. The selection process was less than scientific (most of these games are said to have had Nazca staffers involved, although there's more I checked like Mystic Riders which had nothing) and even with a source for members of Nazca (specifically the credits from Neo Turf Masters, Metal Slug and Metal Slug 2- I chose not to include the staff lists for Metal Slug X or 3 as I felt they were too far removed to be helpful and they might've caused confusion) it wasn't that easy. Figuring out a pseudonym from just three letters on a high score table takes a bit of guesswork, so this listing is far from 100% accurate. However, it's certainly something, and it might help quell one or two assumptions. 'Cause when you say 'from the creators of Metal Slug!' you're implying a lot which can be deceptive, as we shall see.

I've only put names on this list that I could connect to Nazca staffers, so it's not the full staff list for each game.

If you want to see the full staff listings, click the source (high score table or staff roll) underneath each game's title.

Finally, names on the Nazca side with (?) next to them are just educated guesses, such as Ken in Hook possibly being Ken-Kui.

On with the list.

Irem Game + Source Staff Name in Irem Game Staff Name in Nzaza Game

Air Duel
(High Score Table)
Kire-Nag / Kazuma Kujo (?) [MS]
Andy / Kenji Andoh [MS, MS2]

Hammerin' Harry (US)
Daiku no Gensan (Japan)
(High Score Table)
Lucky Susumu
Gangy Hiya
Susumu [MS, MS2]
HIYA! (?) [MS, MS2, NTM]

Major Title
(High Score Table)
Kinte [NTM]
Max.D / Kazuhiro Tanaka (?) [MS]
Andy / Kenji Andoh [MS, MS2]

Cosmic Cop (US)
Gallop - Armed Police Unit (Japan)
(High Score Table)
Kohdoh (?) [NTM]

(Staff Roll)
Ken-Kui (?) [NTM]
Kon. Kitakichine (?) [NTM]
Kozo [MS, MS2, NTM]
Andy / Kenji Andoh [MS, MS2]

The Irem Skins Game (US)
Major Title 2 (Japan)
(High Score Table)
Zen [MS2, NTM]
T. Yokota / Tetsuya Yokota [MS]
Max.D / Kazuhiro Tanaka[MS]
Tomohiro [MS, MS2 (as Tomo)]
Hirokun [NTM]
Ken-Kui [NTM]
Kinte [NTM]

Undercover Cops
(Staff Roll)
Meeher [MS, MS2]
Akio [MS, MS2]
Kozo [MS, MS2, NTM]
Susumu [MS, MS2]

In the Hunt (US)
Kaitei Daisensou (Japan)
(Staff Roll)
Ken Kui
Akio [MS, MS2]
Susumu [MS, MS2]
Tomohiro [MS, MS2 (as Tomo)]
Kozo [MS, MS2, NTM]
Ken-Kui [NTM]
Kire-Nag / Kazuma Kujo[MS]
T. Okui / Takeshi Okui[MS]

Ninja Baseball Bat Man
(Staff Roll)
Ken Kui
Kon. Kitakichine [NTM]
Hirokun (?) [NTM]
Meeher [MS, MS2]
Ken-Kui [NTM]
Hamachan / Shinichi Hamada [MS, MS2]

Superior Soldiers (US)
Perfect Soldiers (Japan)
(Staff Roll)
Kire-Nag / Kazuma Kujo[MS]
Hirokun (?) [NTM]

Some further notes to go with that table.

First, as well as plenty of other info, reader Kino asked Mitsuo Kodama about ANDOH in Air Duel so that's where that info comes from.

Next, one name seen in a Nazca game that bears mentioning is T. Nishiyama, listed as 'Boss' in Neo Turf Masters and 'Produce' in Metal Slug 2.

This is almost certainly Takashi Nishiyama of SNK, famous for creating Fatal Fury and Art of Fighting.

His name here is probably here, as Youloute pointed out, due to Nazca always being part of SNK.

Two obvious games are missing from that little chart- Gunforce and Gunforce II.

Both of these games clearly share staff members- the original Gunforce perhaps not so much, but Gunforce II/Geostorm has that distinctive graphical style of the team. However, both the Gunforce games lack a staff roll and none of the names hidden in the high score table (here's Gunforce's table and Gunforce II's table) match up (except possibly YA! in GFII which might be HIYA!) However, Kazuma Kujo himself confirmed, in a roundabout way, that Gunforce II was worked on by certain Nazca members in that Retro Gamer article, so there you go.

And now a bonus section with development details on several Nazca games from the Retro Game Test videos (here and here again) kindly translated by Youloute.
Additional info in the Where the Staff Members Went section courtesy of Kino.

Undercover Cops
Shmuplations has an odd interview with Meeher and Hiya! about this game, and they also translated the Undercover Cops manga!

In the Hunt
Tobi_Nag/Kire-Nag/Kazuma Kujo didn't choose to work on a shmup. He didn't want to make a game with a forced scrolling either.
Okui, an R-Type fan, was recruited while the development of the game had already started but did almost nothing on it, as he had been asked to work on Gun Force 2 shortly after joining Irem.
At first, there weren't submarines but spaceships which were moving under the sea. Akio did the art for the submarines after a few Irem developers left the company.
Hiya! originally was in charge of the BGM but he was working on Image Fight II at the same time and it took too much of his time- he spent a whole month in a music studio for it, days and nights. The man who did the music for In the Hunt wasn't really appreciated by his colleagues, though. It was his first solo porject at Irem but he didn't stay long in the company.
There is also a related manga.

Gunforce II / Geo Storm
During the development of the game, the dev team knew that its deadline was also the closure date of Irem's arcade division. They knew that Irem would no longer develop arcade games so they planned to quit Irem after the completion of the game.
2 game designers were working on the game but their work wasn't satisfying and the game had already been delayed- the game was originally planned to be released before In the Hunt.
The graphics weren't very good either, especially for the characters but they only had the time to redraw the backgrounds and add the motorbike sections in which the sprites used for the main characters look significantly better.
One of the designers who has been asked to redraw the graphics was Okui. He was working on In the Hunt but Irem asked him to work on Geo Storm in order to save the game from cancellation.
Due to a lack of time, Hiya! reused the music he composed for Air Duel in Gun Force 2 - his boss allowed him to do so. (A track for Air Duel, Mission 2, would also serve as the basis for Livin' on the Deck from Metal Slug 2).
From January 1994, the employees of the arcade division were no longer required to work in Irem's offices. Only 3 developers were still coming: Meeher, Okui and Atsushi Kurooka.
The game is hard because the people tasked to playtest it ware hardcore gaming fans who were always asking to increase the difficulty.

Metal Slug: Super Vehicle-001
The development of the game started while Nazca was porting SNK games to various consoles. Tobi_Nag/Kire-Nag/Kazuma Kujo was the director of the original version, Meheer came later, probably after the first location test. It seems Nag wasn't really happy with all these changes at the time.
Remember the August 1995 location test in Osaka we mentioned? This was a very different take on the game! This version featured tanks as playable characters (so no Marco or Tarma on-foot) and received a mixed reception. Nazca planned to include 6 levels in this version but the Kobe earthquake prevented Akio to come to work during its development.
The 2nd level of the final version was specifically designed for the second version of the game in which the main characters weren't always inside tanks. This late addition explains why the second part of this level doesn't have its own music - it reused the music composed for the 3rd level. The music composed for the first version of the other levels was sped-up for the second version.
Almost every level was expanded since the developers thought they were too short for a console game (it seems they were already planning to port their game to other machines). The backgrounds created for Missions 1 and 3 were redesigned in order to give the game an overall lighter look, with more cliffs in the background of Mission 1. Mission 4 is the only one which wasn't modified during the development of the 2nd version.
When asked if the designer of the tank was influenced by Masamune Shirow's Dominion Tank Police, no answer was given.
As a side note on character names, the 2 main characters of the first Metal SLug were originally called Phil John and Michiko Nakajima. Additionally, Youloute said that they may have chosen to name two of the main characters of the series Fio and Marco as a reference to Hayao Miyazaki's Porco Rosso (Fio Piccolo and Marco Pagot). Additionally, Kazuma Kujo would later mentions Miyazaki as one of his main reference for Steambot Chronicle, a game partly developed by former Nazca developers.
Parts of the stuff designed for the first version are still in the ROM of the retail version, including the golden tank used in 2 player mode (which is also featured at the beginning of Mission 6), and tied-up Morden soldiers that were originally going to be P.O.W.s you could free (they would have a blue palette), who were replaced by the classic beardy P.O.W.

Where the Staff Members Went
Tobi_Nag / Kire-Nag / Kazuma Kujo left SNK for Irem shortly after the end of the development of the first Metal Slug. He then worked on R-Type Delta and founded Granzella.
Kozo, Hamada, Hiyamuta, Tetsuya Yokota and Hiroshi Yamada would all work on Dolphin Blue at Sammy in 2003.
Susumu left the games industry to become an analogue illustrator.
Hamachan worked at Sammy for many years and now works as a freelance VR game designer.
Meeher left the games industry after Metal Slug 3.
Akio left SNK in 2010, ocassionally providing freelance illustration work for games like Street Fighter V.
T. Okui / Takeshi Okui left SNK during the development of the first Metal Slug, after the completion of the first version, and later went on to be a graphics artist for games like Final Fantasy VII, Xenogears & The Legend of Zelda: Breath of the Wild.
Max. D / Kazuhiro Tanaka went back to SNK to do art on their mobile games.
Hiya! was director of the sound team at SNK until he left the company in 2000.

To end on an amusing note, there's a name in the Undercover Cops credits under American Staff- Drew.

This is actually Drew Maniscalco, one of the founders of Irem's American branch who created Ninja Baseball Bat Man.

I sent him an email once pestering him about Undercover Cops' weird US downgrade.

And he replied, which was amazingly polite considering the text wall I'd sent him.

Just thought I'd share, is all.

A million thanks to Youloute and Kino whose contributions and translations were invaluable.

Can you fill in any more gaps on this chart, dear reader?

If you can, we implore you to get us on the horn, either via email (TheMetalSlug at gmail dot com) or on the Twitters.

I'm never doing this kind of nonsense again.