After losing everything she's worked for and with the war for Etheria seemingly over, a barely unconscious Catra is wallowing in guilt and self-loathing when a odd vehicle appears in front of her. With nothing left to lose, Catra boards it and soon discovers that she's the newest passenger on the Infinity Train, an extra-dimensional Epiphanic Prison that will only let her leave once she's solved all her problems. Thankfully, she isn't alone, as she soon meets another new passenger by the name of Steven Universe, who has boarded the train thanks to his life also being in the midst of falling apart. Deciding to become companions, the duo work together to explore the train, making friends and enemies as they struggle to return home.
Meanwhile, the worlds they have left are spinning along despite their disappearance. How exactly will Adora and the Rebellion fare in the fight against the intergalactic Horde Armada if Catra isn't present to pull a HeelFace Turn and begin aiding them? And how will Beach City and Gem Homeworld cope when they realize Steven can't be found anywhere in the galaxy?
The story is ongoing.
Peace of Mind, Piece of Heart contains examples of:
- All-Loving Hero: Steven retains this quality from his home series, being incredibly amicable to every denizen he and Catra encounters.
- All of the Other Reindeer: Butter Brickle, a popsicle child, is shunned by his community not only because he managed to survive a violent passenger raid that claimed the lives of many others a few years ago, but also because he continues to befriend all the travelers that pass through the train car.
- Alternate Dimension: Steven theorizes that the train both exists in one, as well as picks up travelers from various others, when Catra shows no familiarity with the Gem Empire.
- Beyond Redemption: Invoked. Catra rebuffs Steven's attempts to learn more about her on the basis that she's guilty of far too many atrocities to deserve any sort of kindness.Catra: "Dammit! Dont you know a lost cause when you see one?"
- Cat Folk: Catra, with Steven excitedly calling her a cat girl when first meeting her, much to her embarrassment.
- Call-Back: To numerous events in She-Ra and the Princesses of Power and Steven Universe, naturally. For example, when explaining reasons why Steven shouldn't want to get close to her, she specifically mentions opening "portals that nearly destroy reality" and ruining "stupid, stuffy proms".
- Damsel in Distress: Glimmer is trapped in a Gilded Cage, but unlike in canon, Catra is no longer present as a sympathetic ear or comrade.
- Epigraph: Every chapter begins with one of these.
- Foil: Catra and Steven serve as this to each other. The former is an AntiVillain, grew up as The Un-Favourite, is a jerkass who secretly cares deeply about others, and revels in using violence when she has the chance. The latter is an undisputed hero who grew up being loved and supported by pretty much everyone he meets, and is in turn an extremely kind and empathetic person (who secretly holds some negative thoughts he'd desperately like to ignore), and will always go the pacifist route unless there is no other option.
- For Want of a Nail:
- The fanfic takes place during the final season of She-Ra, with Catra boarding the train taking the place of her and Glimmer's confrontation, and thus their combined abduction, at the end of season four. The B-plot of the fanfic explores what has changed as a result of her absence.
- The fanfic also takes place towards the end of Future, after the events of the episode "Mr. Universe'", with Steven boarding the train taking the place of him running away to train under Jasper in the following episode.
- Heroic B So D: Steven suffering from this after having an apparent falling out with both his girlfriend Connie and his father Greg in the days prior is what summons the Infinity Train to him.
- Idiosyncratic Episode Naming: Mirroring Infinity Train, each chapter follows a "The [Noun] Car" format.
- Ignored Epiphany: Catra pushes a little cat girl named Marmalade down a slide to help her get over her fear of the slide; Marmalade gets hurt and becomes afraid of Catra instead. Even though Marmalade was hurt and crying, and her friends Mochi and Rascal call out Catra for what she did, Catra just runs away, denying to herself that she did anything wrong.
- Jerk with a Heart of Gold: Despite her jerkass behavior, Catra does attempt to cheer others up when they're feeling down, and at one point she immediately apologizes to Steven when she realizes one of her quips struck a nerve.
- Late-Arrival Spoiler: Don't read this fic if you didn't finish watching She-Ra (2018) and Steven Universe Future. The Reveal at the end of Infinity Train Book 1 is also immediately spoiled.
- Love Epiphany: Bow tells a sleeping Adora that he has retained memories from the third season's Lotus-Eater Machine, and one of them includes a moment when he and Glimmer shared a kiss, making him realize that he has romantic feelings for her and wonder if Glimmer also remembers and feels the same.
- Obviously Evil: When Catra states that, while she figured it out pretty quickly, no one in the Horde really thought of themselves as "villains or anything", Steven points out that they literally lived in a place called the Fright Zone.
- Ontological Mystery: Averted. Since this takes place after Book 1 of Infinity Train, Catra and Steven are fully aware of the train's purpose and the meaning of the numbers thanks to One-One's introductory videos. However, they're still at a complete lost as to how to accomplish the "fix their problems" part of the equation, and Steven is flustered about how the train functions in general.
- Pet the Dog: One of Catra's first actions on the train. Though she's at first indifferent to Butter Brickle, who was showing her the way to leave the car, she become sympathetic to him when he reveals that he's an outcast with no friends. Catra encourages him to stand up for himself, even agreeing to be his friend regardless of whether they actually see each other again. Her number comes down for that act of kindness.
- Reformed, but Rejected: Discussed. When talking about the broken pedestal he now holds for his mother, Steven muses that redemption is different than forgiveness. When asked by Catra to elaborate, he explains that while one can definitely work to become a better person, no one is actually obligated to forgive you for everything you've done prior to that; by the same token, people can forgive you even if you think you don't deserve it.Steven: "Redemption is you and forgiveness is them, basically."
- Riddle for the Ages: Steven unloads several of these about the train, mainly concerning how the train cars move and the general capabilities of the train such as its possible ability to access other planets and dimensions. Catra throws in her own guesses after Steven prods her for input, but could care less for the most part.
- The Short War: According to Steven, when he first entered The Chocolate Car, four kinds of chocolate were in a long-standing civil war. Steven managed to end the conflict in a week. Catra, who herself just came from the middle of a decades-spanning conflict, is incredulous.Catra: "So, yeah. How did you end a war in a week? Positive energy and the power of friendship?"''
Steven: "Kinda, in part. Also some reconstruction, halting a few battles, saving some bystanders. It was a process."
- Screw This, I'm Outta Here!: Catra pushes a little cat girl named Marmalade down a slide to help her get over her fear of the slide; Marmalade gets hurt and becomes afraid of Catra instead. When Marmalade's friends Mochi and Rascal call out Catra for what she did, and a crying Marmalade asks why she did it, Catra runs away in anger.
- Tantrum Throwing: Bow does this when he fails to prevent Glimmer's abduction, angrily shooting his arrows at the sky before breaking down in tears.
- Tough Love: Deconstruction. Catra attempts this with a cat girl named Marmalade she meets in her second car, forcibly pushing the scared child down a large slide. The kid gets hurt in the process, with Marmalade's friends and the child herself, calling out Catra for her unnecessary violence, causing Catra to run away out of guilt.
- Tranquil Fury: Downplayed. Horde Prime's reaction when Glimmer attempts to escape in Chapter 2 is more annoyance than anything, but it's still enough to make him switch tactics from what would have been a non-violent interrogation session to torture.
- Two Lines, No Waiting: So far, Steven and Catra's adventures on the train have been juxtaposed with the events of She-Ra season five.
- Villainous BSoD: Catra suffering from this after receiving a "The Reason You Suck" Speech the end of "Destiny: Part 2" is what summons the Infinity Train to her.
- What the Hell, Hero?: A little cat girl named Marmalade's friends Mochi and Rascal call out Catra for pushing Marmalade down the slide and getting her hurt. Catra justifies herself by saying that she just pushed her down a slide. Mochi fires back that that's not the point, and that she hurt Marmalade and made her more scared than she already was. When Catra continues to deny she did anything wrong, Marmalade tearfully asks Catra why she did it, causing Catra to run away in anger.
- You Remind Me of X: Steven's bright colour scheme and use of magic has Catra mentally associate him with Glimmer, right down to giving him the nickname "Sparkles". Steven saving her after nearly hurting her during a Diamond outburst also has her think of her complicated relationship with Adora.
- You Wouldn't Like Me When I'm Angry: Like in Future, Steven's diamond abilities manifest when he's overwhelmed with emotion. Nearly getting injured on an assembly line in The Gear Car triggers traumatic memories of getting stomped on by Yellow Diamond which causes his powers to go berserk and destroy the entire factory.