OK, I'm cheating here. There isn't much to say about Undertale from a "feminist fiction" perspective. At least, not without spoiling the game, which I really don't want to do.
But Undertale is an absolutely amazing game, and I simply had to write about it. Don't let that simple pixel-y look deceive you. Undertale is funny, fun, surprising and emotional. It'll probably make you cry, and it will definitely cause you to get far too invested in a bunch of little 8-bit monsters.
In Undertale, you play a gender-neutral human child who has fallen into the underground realm of monsters. You must pass safely through this world to find the barrier between the realms and return safely home. As you go, like in most RPGs, you encounter monsters and bosses to fight. You can get items and armor to make you stronger, and you can bring down everyone you meet.
But you can also choose not to fight. All enemies have a reason for attacking you, and if you can convince them to stop, you can spare their lives and continue on your way. Put in the effort, and you might even make friends. You might even end up on a date with a skeleton.
But this isn't a simple choice of "killer path" or "peaceful path." Pacifism is difficult. The game always gives you a hint about how to resolve things peacefully, usually through character dialogue, but they're not always easy to figure out. And if you never kill anyone, you never gain XP, meaning you face stronger and stronger monsters with the same health, attack and defence as when you began. When an enemy has killed you for the tenth time, it can get tempting to just hit back.
And of course, there's the question of whether you want to be a pacifist all of the time. Sure, it's easy to spare the cute fluffy dog or the nice woman who baked you pie, but if the enemy has done awful things, do you want to spare them? Is it even safe to do so? Character actions have consequences, and although the game starts with a sense of "tra la la, love and kindness," it gets far more complicated along the way.
But killing enemies has consequences too. If you start marching through the world of monsters killing everyone you encounter, characters will react to that. The whole story will change. You are, after all, a rampaging murderer to these creatures. It's a horror story, and you're the monster.
If players play either of these two extremes, they'll experience almost entirely different stories, even if the basic steps are the same. But there are also many paths in middle, where you befriend one person but kill another, do this but don't do that, that also reshape the story.
And multiple runs are encouraged. Things might not all go as you've intended, and the game doesn't completely reset when you restart it. Some memories linger in the characters, and more of the story is revealed. I was told this by a friend on my first playthrough, but although I was enjoying the game, I couldn't imagine wanting to replay it -- I'd just get it right the first time. Then I actually got to the end, and immediately started the game again.
That said, the game I'm recommending is the peaceful game -- the game I assume most people try to play at first, if only because that's that game's selling gimmick. Undertale's greatest strength is its characters -- how much personality they have, how quickly you grow attached to them, how you might suddenly find yourself crying a not-so-digital tear when you learn more about who they are. Having finished two runs of the game, killing any of them seems too emotionally gruelling to attempt. Even watching a Let's Play of that path on Youtube was difficult, to say the least.
After two runs and some videos, I'm sure I still haven't seen all the possibilities in the game. It starts off deceptively light and simple, but there's a lot hiding underneath, and something about its simplicity makes it particularly emotionally compelling.
And don't worry if, like me, you're not a fan of RPG turn-based combat. Undertale makes it far more interesting, first by having you figure out what peaceful approach is best for each enemy, and second by having a mini-game for each enemy's attack -- if you can dodge them, you don't take any damage. And the enemies not only all have unique attacks to dodge, but attacks that change depending on what you do. An angry or distressed enemy will attack faster. An uninterested or sad enemy might not really try to hit you at all.
Overall, Undertale is a game that starts out cute and funny, but quickly sucks you in. It only takes six or seven hours to initially play, but it will stick with you for much longer than that.
I have so much I could say about this game, the cleverness of the writing, the world-building and the characters and the directions it takes. But I also don't want to spoil a thing. Go into this one blind. Give it a try, and see where it takes you. I promise it'll be worth it.