I've been vaguely aware of the Atelier series since the PS2 era, though they've been around a while longer than that, but this is the first one of them I've actually played (well, I did play the spin-off Mana Khemia on PSP many years ago, but they're different enough that I can call this the first). With that in mind, I don't know all of the dfetails, but I think this is a sequel to another Marie no Atelier that was on consoles, and has you playing as the eponymous alchemist in her post-adventuring days.
Marie now runs a little alchemy shop (or Atelier, if you will) in a nice walled city with European-style buildings, making the whole affair somewhat reminiscent of Kiki's Delivery Service. One day, she's given custody of a little fairy boy, who she's going to teach alchemy and generally look after for four years. So, rather than a traditional RPG, this is, like the in-game alchemical syntheses, something like a combination RPG, business management, and even a tiny bit of Princess Maker. There are dungeons and combat, but you just send the fairy out to do those things (you can hire bodyguards and buy him better weapons and armour to help him though) and fetch back items for you.
So what do you actually do, if you're outsourcing the dungeons and combat? You go to the bar to accept requests for items, then you either have to get the required items from a dungeon, or synthesise them in your Atelier. Despite Marie presumably being a veteran of the business, and the one you're controlling, you can only syntheise items up to the skill level of the fairy. This is advanced by making the recipes to which you do have access, by handing in requests, and by buying textbooks from the local university.
Sometimes certain special events happen, like Marie's birthday, or the fairy going off to celebrate fairy new year with his family. There's also more unique and dramatic events too, like the fairy nursing an ill Marie back to health, or the fairy becoming depressed and surly, gradually being brought back to his normal cheery self through the aggressive application of love and care from Marie. Those descriptions might sound a little cynical and dismissive, but those moments were actually really nice, and I feel like this kind of emotional warmth isn't something you often see in videogames, especially ones on 8-bit hardware.
This is a fun and engrossing little game, that's definitely worth your time. You can tell the developers really tried their hardest to get the best game they possibly could out of the Game Boy Color, and their work totally paid off. This is easily one of the best games on the system, and while it's understandable why it never got an official translation on its release, it's still a shame that that didn't happen. Fans have, of course, stepped in to correct that mistake more recently. At the time of writing, I've only played through three of the game's four years, and once I'm finished, I'm probably going to look into the series' main entries too. It's especially recommended to those kinds of people who talk about wanting "cosy games", as it's definitely one of those.