Riverhillsoft's 1988 PC-88 mystery Kohakuiro no Yuigon just hit the Switch

D4 Enterprise has released the 1988 PC-8801mkIISR mystery adventure game Kohakuiro no Yuigon (The Amber Testament) for the Nintendo Switch. The port launched today as part of the EGG Console series and is available on the Japanese eShop for 880 yen (and $6.49 in North America).

Developed by Riverhillsoft, the studio that previously created the J.B. Harold Murder Club series, the game is a classic command-based adventure. Players take on the role of private detective Ryunosuke Todo in 1920s Japan. He is hired to investigate the poisoning of a wealthy merchant at a sprawling estate called the Kohaku-kan.

Mapping the mansion

The victim's only will consists of mysterious western playing cards. To solve the case, players have to navigate the mansion and interview a large cast of family members and staff. The game does not hold your hand. You have to manually select commands to move between rooms, talk to people, and examine objects.

The investigation relies heavily on tracking complex human relationships. Players use a dedicated relationship chart to organize suspects and motives. An evidence screen lets you analyze physical clues like lace handkerchiefs and dropped items. The entire game is presented in a sepia-toned pixel art style that matches the 1920s Taisho era setting. The PC-8801mkIISR was equipped with a Yamaha YM2203 FM synthesis chip, which Riverhillsoft used to create a moody soundtrack. The EGG Console emulator replicates this audio hardware faithfully, complete with the distinct metallic twang of 1980s FM synth.

According to the eShop listing, the core game and gallery remain entirely in Japanese. D4 Enterprise translated the emulator menus and basic instruction screens into English, but you will need to read Japanese to actually solve the mystery. The publisher also notes that USB keyboards are supported if you want the authentic 1988 input experience, though they only guarantee compatibility with Japanese 106, 108, and 109 key layouts.

The Riverhillsoft catalog

Riverhillsoft was a major player in early Japanese adventure games. Before they shifted to console survival horror with games like Doctor Hauzer and OverBlood in the 1990s, they built their reputation on computer mysteries. They were also responsible for the Japanese computer ports of Prince of Persia, which gave the protagonist his familiar turban and vest design.

Kohakuiro no Yuigon originally launched in 1988 before getting ports to the MSX, X68000, and Windows. This Switch version runs via D4 Enterprise's proprietary emulator wrapper. The company has spent the last few years bringing dozens of similar Japanese microcomputer games to modern hardware through the EGG Console label. Their catalog covers everything from action RPGs like Ys and Relics to obscure text adventures. The Switch has quietly become an excellent platform for exploring this specific era of Japanese PC gaming.

It is a highly specific slice of 1980s computer history. Buying original PC-88 hardware and floppy disks in 2026 is an expensive headache. Floppy disk rot is a real problem for games of this vintage. Digital re-releases are one of the only reliable ways to play them today. Having direct eShop access to Riverhillsoft's early catalog saves you from dealing with aging magnetic media and expensive Yahoo Auctions listings.