(Note: Screenshots are of the PC-88 version, but the FM-7 version is the original)
August 1984 really was the month that Japanese adventure games took a leap in graphical fidelity. This along with Eiyuu Densetsu Saga made strides in scanned-in art (though as I understand it different ways of achieving this) to create convincing anime-style art for adventure games. While Eiyuu Densetsu Saga is also known for being an early (perhaps even first! depending on your definition) menu-based adventure game, Zarth is mostly remembered for just its art, particularly the last image above, the pink-haired Mirika, prominent in the game's advertising (ironically Mirika only appears in the prologue and the girl in your party for most of the game, Torald, never gets a graphic of that detail). At least that's all I knew about it, so everything else in the game was all new to me. What I found was a game that was surprisingly thoughtful in its design with ambitious storytelling for the time.
Some interesting development context from the Game Preservation Society: the game was developed by a team of high schoolers known as Studio Jandora. The director, Tadashi Sugie, got into computers after a middle school volleyball injury, eventually submitted a game to Enix's second Hobby Program Contest, and was then made lead of this team. Some members of the team went on to do notable work, like Yoshinori Sayama, who would go on to do mechanical design for anime like Patlabor and Char's Counterattack.
(Note: Some names I could only find in Katakana, so apologies if my transliteration is different from other sources)
Zarth takes place 100 years after a nuclear apocalypse carried out by the American superweapon Orion and the scientist Bittner. 4500 survivors awakened from cryosleep and began to build villages to resume life. You play as Zarth who lives in the village of Rimanon. One day, a girl named Mirika (the girl from the famous image) comes to inform the village chief that her village was destroyed. The village chief suspects Nava is behind this and asks Lando, Torald, and Zarth to get to the bottom of this. It is too late, as that night Rimanon is attacked by Nava. Only Zarth and Torald escape to the forest, where the game begins.
For some reason I always thought the game was sci-fi fantasy, but it turned out to be post-apocalyptic cold war sci-fi. Throughout the game you learn more about Nava and what plot is being carried out. It is of a larger scope than previous Japanese adventure games, and while I respect the ambition, it wasn't for me.
Ending Spoilers
The twist that Lando is actually the villain just didn't hit for me. They try to make it worth it by having him give his backstory before the final section of the game to try to endear you to him so the betrayal feels more impactful. Didn't care lol
What ended up being a pleasant surprise was its puzzle design and parser. The function keys list nouns, verbs, and locations you can use which help cut down on figuring out what actions are possible. Characters in your party offer hints if you do enough actions that don't move the game forward. Important words are highlighted in the text. Also some puzzles seem to be kind of "invisible" inventory puzzles. Where you need to have an item/character to pass an event, but you don't need to put a command to use the item. Like there's an event that I'm pretty sure if you didn't have the item/character in your party it would've been game over, but if you do it automatically proceeds the story. So it streamlines the game to rely less on the parser, but the tradeoff that you might not know what you needed to have to solve a puzzle. Even the traditional inventory puzzles it has are pretty intuitive, sometimes even accepting multiple verbs rather than just one, and along with the helpful features above makes for an overall easier adventure for the time.
One novel mechanic is there is a day/night cycle, which restricts certain areas at night so you'll need to sleep. It doesn't really come into play much, but still an interesting addition.
All in all, Zarth had a lot more going on underneath the popularity of that one graphic.