The Unwavering Light of Calamity
is an Amphibia and The Owl House crossover story, in which Luz's older sister Lucia goes to stay with her godparents, the Boonchuys, after graduating high-school, and ends up sucked into Amphibia with Anne, Sasha, and Marcy.
- Adaptational Name Change: Maddie Flour's full first name in this story is "Madness".
- Adapted Out: The plots of a number of episodes never happen in this AU thanks to Lucia being present.
- Alternate Self: After meeting Amity and noticing her similarities to her old crush Amelia (both in name and appearance), Lucia thinks back to what Frog Soos said, implying that the two are dimensional counterparts of each other despite the age gap.
- Ascended Extra:
- Maddie Flour's friendship with Lucia means that she has significantly more focus than in canon, even joining the Plantars and human girls on the trip to Newtopia.
- The Calamity Box in the Owl House basement is found by Maddie, and it has a yellow gem, with the implication that it'll have further impact on the plot than just a one-off joke.
- Big Sister Instinct: Lucia takes her position as an older sister seriously, as reflected by how she acts as a sister figure to Anne, Maddie, and Ivy. Also, older siblings who don't take their role as seriously are something of a Berserk Button for her.
- Brain Bleach: When Lucia realizes that she likes people with bright-colored hair after seeing Odalia, Lucia realizes that Amity has bright hair, and has to fight the urge to throw up and punch herself in the face for thinking that.
- Cliffhanger: Act 1 ends with the fight in Andrias' throne room over the Calamity Box causing it to open and send Lucia to the Boiling Isles, depositing her on the Knee in time to witness Amity getting attacked by the Slitherbeast.
- Contrived Coincidence: For some reason, when Lucia and Maddie are sent to the Boiling Isles, they're right by Luz and Amity when they're attempting to deal with the Slitherbeast.
- Decomposite Character: Lucia is based off of Luz's "Beta" design, but exists separately as the girl's older sister.
- Et Tu, Brute?: Lucia takes The Reveal that Marcy is the one who got them all sent to Amphibia very badly, due to seeing her like a sister.
- Excellent Judge of Character: Lucia is very good at reading people. Just for starters, she easily sees through Sasha's manipulative tendencies, having tried to get Anne and Marcy to get out from under her thumb pre-Amphibia, and gives Valeriana the benefit of the doubt when letting her hold the Box because she didn't feign ignorance like Andrias did.
- Fantastic Racism: A journal entry from Samuel Newton, an ancient newt scientist who created the Core, depicts how he looked down upon the other Amphibian races and was disgusted by the idea of a merged culture between them.
- Fantasy Pantheon: The Amphibians worship a pantheon called the Divine Triumvirate, composed of the God Frog (who favors farmers), the Holy Toad (who favors warriors), and the Saint Newt (who favors scholars). Apparently the three were separate faiths before Amphibia's three main races were unified.
- Gladiator Games: Grime sentences Lucia to these during the takeover of Newtopia, in order to test her as a Worthy Opponent.
- Has a Type: After seeing Odalia Blight and finding her attractive, Lucia realizes that she has a thing for people with bright-colored hair.
- He Knows Too Much: When Lucia reveals during the throne room confrontation that she knows that Andrias has a master, he immediately decides that she needs to die for knowing too much.
- Hero of Another Story: Most of Anne's adventures still happen offscreen while Lucia is off doing her own thing.
- Hero with Bad Publicity: After Lucia meets Luz again, we learn that it's assumed that Lucia kidnapped Anne, Marcy, and Sasha after the four of them disappeared.
- I Have Your Wife:
- Valeriana kidnaps Lucia as part of Anne's Secret Test of Character at the second temple.
- During the Toad takeover of Newtopia, Grime forces Lucia to agree to fight in Gladiator Games by threatening Maddie (who isn't off limits like Anne and Marcy are).
- Innocently Insensitive: When Lucia tries to stop Wartwood's shipping war over Love Choice in its tracks by suggesting getting rid of the female character (whom she found utterly unlikeable) and just getting the two males together, the town tells her that she's being stupid because guys can't date each other. This causes the closeted Lucia to assume they're all homophobic, and she angrily chews them all out before stomping off; it's only later that she learns that Amphibia (or at least the provincial Wartwoodians) don't have a concept of homosexuality and literally didn't understand how two guys can be romantically involved. Once it's explained to them, they apologize for upsetting her (and also agree with her assessment of the pairing).
- I Never Told You My Name: After Littlepot hitchhikes with Lucia while she's driving Bessie back to Wartwood, he bids her farewell using her full name... when she was careful not to say it to him. Needless to say, she gets spooked.
- In Spite of a Nail: Despite Lucia's presence, some events play out more or less the way canon did.
- Despite Lucia being sent to find Anne, the Box still gets opened and the girls sent to Amphibia.
- Since Lucia doesn't join the Plantars and Anne in attempting to make pizza, they still lose.
- Luz still ends up chasing Owlbert into the Boiling Isles.
- Polly still meets and befriends Frobo.
- Loving a Shadow: Maddie had a crush on Sprig, but after actually travelling to Newtopia with him she realizes that the "Sprig Plantar" she liked didn't really exist.
- Magical Species Transformation: Maddie's mother Wisteria is capable of brewing a potion than allows her to change into a newt, frog, or toad, which she uses to blend in when traveling and selling her wares (for instance, she's a newt in Newtopia). When asked which race she was originally she doesn't say, and apparently she's been in other forms as well.
- Noodle Incident: Whatever Lucia did to Toadstool and Toadie to punish them for spraying Anne's eyes during the bugball game, the Mayor still gets nightmares weeks later.
- Oblivious to Love:
- Sprig had no idea that Maddie liked him until she's telling him that she's over those feelings.
- Lucia, while normally rather perceptive, is rather thrown by Amity's similarity to her old crush Amelia, and that combined with noticing Amity's burgeoning crush on Luz causes her to completely miss that the younger witch has a massive puppy crush on her, thinking that she's just shy instead.
- One Degree of Separation: In this AU the protagonists of both Amphibia and The Owl House are connected, with the Boonchuys being the godparents of Luz's older sister Lucia.
- Only Sane Man: While Lucia has her vices and flaws, she's still got the most common sense out of the main characters, with several episodes never happening because of her presence. Case in point, she easily spots Sasha's manipulations and tries to get Anne and Marcy to do things without her.
- Our Vampires Are Different: Snakeshifters are a kind of Amphibian monster that are highly vulnerable to light and feed of the blood of frogs, shapeshifting to blend in and lure in their prey to their underground lairs.
- Precocious Crush: Amity develops a crush on Lucia, who is a few years older than her and Luz, after she helps save her from the Slitherbeast.
- Properly Paranoid: Lucia is very careful with keeping the Calamity Box safe and hidden. Given both what Andrias wants it for and how Hop Pop buried it in canon, not an unfounded concern.
- Sailor Earth: While all evidence is that Lucia has a yellow Calamity power, the Box still has just the three canon gems. An old piece of paper and a broken shield at the Bizarre Bazaar both imply the existence of a fourth gem that was stricken from the records for some reason (the piece of paper having a red X over a yellow image and the shield missing a piece), but details still remain sketchy. Once Lucia and Maddie end up in the Isles, the latter finds the second box with a yellow gem in the basement of the Owl House, seemingly proving that it does exist, but the details are still sketchy.
- The Scapegoat: When the subject of how the toads bully and harass the frogs comes up thanks to Lucia during the Plantar's first meeting with the king, Andrias throws the Newtopian emissary Jacinda under the bus, the notes making it clear that he has no intention of dealing with the issue, which he already knew about.
- Tragic Keepsake: Lucia's army jacket was a gift from her father, and she's almost never taken it off since he died.
- We Used to Be Friends: Ivy and Maddie were best friends when they were little, until Maddie started focusing more on first caring for her sisters, and then on her magic research. Ivy eventually got so desperate to get her attention back that she started bullying her, on the grounds that negative attention was better than none. Once she admits this in the present, and Maddie acknowledges her own part in their friendship falling apart, they agree to start working towards rebuilding what they had.
- What If?: The core concept of the AU is that Luz has an older sister named Lucia, who decides to stay with her godparents the Boonchuys after graduating highschool, causing some changes to canon.
- Barry avoids getting tripped and dropping his berries, so he never curses Anne and Sprig.
- Lucia talks Anne out of her over the top plans for the Frog of the Year party, so things go a lot smoother.
- Instead of Anne and Sasha's Rooftop Confrontation at Toad Tower, it's instead Lucia vs Grime.
- Maddie ends up joining the Plantars on their trip to Newtopia to visit her mother, a traveling apothecary.
- The fight with the Barbari-ants goes a lot smoother, as Lucia talks Anne down from being overprotective of Marcy.
- Because Maddie stays with her mother in Newtopia for a few weeks after the Plantars return to Wartwood, she's not there to cure the town from the Chick-a-lisk's attack, so the others have to find a cure in her books on their own.
- Maddie accompanies the group back to Newtopia in order to send Lucia off on her way home personally, and as such takes part in the fight with Andrias.
- Thanks to the Box sending Lucia and Maddie to the Boiling Isles, the two of them find the second box in the Owl House basement, and Amity develops a bit of a Precocious Crush on Lucia after the other girl saves her from the Slitherbeast.
- When the second Box activates, Amity is sent to Amphibia with Lucia and Maddie.
- "You!" Exclamation: Lucia's reaction to Grime showing up with Sasha at the third temple.
