Square Is Turning a Classic Visual Novel Into a Natural Language Processing Tech Demo

A chat log from 'The Portopia Serial Murder Case' depicting two characters discussing a safe. On the left side of the screen is a diagnostic, showing how the game is interpreting the player's commands.

Screenshot by Square Enix

Friday, Square Enix announced a new, free port of its deeply influential, 40-year-old point-and-click adventure, The Portopia Serial Murder Case. This new version will have dialogue powered by AI-driven Natural Language Processing (NLP), where players can type or say whatever they want to NPCs.

The Portopia Serial Murder Case follows the story of an unnamed detective as they and their partner investigate the death of a successful banking executive. The original game was released for Japanese PCs in 1983, and then again for the Famicom in 1985. The PC version relied on a very basic text parser, into which the player could input commands for their character’s partner to execute upon. Commands could contain an object and a verb, allowing for some freedom of player expression, while still maintaining a limited set of actual commands to have to worry about. However, like many games which relied on text parsers, some players were frustrated by their inability to correctly phrase a given command, which, in addition to control issues, led the game’s Famicom release to eliminate the text parser in exchange for a more traditional menu system.

The use of NLP in the latest port is one of the bigger experiments a major video game developer has done with the technology that powers buzzy AI chatbots, but, notably characters in The Portopia Serial Murder Case will not use generative AI to respond. In other words, players can say whatever they want and the game will attempt to understand what their intent is, but the NPCs will respond using prewritten dialogue.

In the game, the simple object-verb system is gone, and is instead replaced with an NLP capable of determining player intent from significantly more complex sentences. The use of NLPs in text parsing adventure games is arguably one of the most compelling, and least controversial, applications of the technology seen in video games to date.

Square Enix refers to the game as an “educational demonstration,” suggesting that this is not only a pitch for the company’s own technology, but for the broader utility of Natural Language Processing in games. Its Steam page goes on to breakdown the technologies on display, with one notable exception that is absent from the game itself: Natural Language Generation, which the company claims to have implemented in a previous version of the game, but which is not included in the current release because they couldn’t find a way to prevent the language model from generating “unethical replies.”

“Unethical replies” does not, apparently, refer to depictions of police brutality, which are not only included in the game but advertised on the Steam page. In one screenshot, the player is shown to have told their partner, Yasuhiko Mano, to beat a suspect, which he then does. Instead, it is likely that “unethical replies” refers to replies which would either break the game, using specific prompts to get an NPC to openly reveal the killer for example, or those that contain discriminatory content. In the game’s Steam description, Square Enix states that, upon developing a version of the technology that is capable of filtering out unethical replies, it would consider reintroducing Natural Language Generation to the game.

“This tech preview originally included a function based on Natural Language Generation technology, where the system would generate natural replies to questions that did not have a pre-written response,” Square Enix wrote. “However, the NLG function is omitted in this release because there remains a risk of the AI generating unethical replies. We thank you for your understanding. We will consider reintroducing this function as soon as our research succeeds in creating an environment in which players can enjoy the experience with peace of mind.

While still a relatively simple tech demo, the choice to use The Portopia Serial Murder Case is interesting. The game never received an English official release, meaning that this tech demo will be most people’s first exposure to one of the most influential games in the history of Japanese game development. Moreover, by choosing The Portopia Serial Murder Case for this experiment, Square Enix may be trying to implicitly tie the influence of a game that arguably birthed the visual novel to the potential influence of NLPs on the future of game development.


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