Despite the author (quite correctly) saying that explanations of riichi mahjong tend to sound like Calvinball, I highly recommend people learn the game if you have some time. There are some good videos on youtube going through it (they are long!), but once you learn how to play it's a ton of fun. A good mix of luck and strategy, and tiles are fun to play with (if you're playing in person).

I’ll guess the computer at the bottom is an NEC PC-98/9801.

What is this supergun the author keeps talking about?

I rather enjoy Mahjong - the actual game, played in person even - and so it's a continuing mild disappointment that so often when a thing says "Mahjong" it's actually just tile matching, or a porn game, or in some cases both.

I played a decent video game rendition of the actual Mayjong - not tile matching, nobody gets their tits out, it matters whether you're actually any good at it - in the 1980s but I had no idea this wasn't a common thing, so I don't even remember the name of the software.