Note: Star vs the Forces of Evil belong to Disney and Sonic the Hedgehog belong to Sega. I DO NOT OWN ANYTHING. This this my very first fanfiction and you all know the rest by now. Now let's continue the story.

Sonic and Star in Adventure in Mewni
Chapter 3 Meet Janna

"Excellent" said Eggman in the command room back in Neo Scrap Brain Zone along side with Seth holding a blue Chaos Emerald in his hand as they communicate with Rasticore via by a big hologram table which projected an image of a very tall muscular with green skin, a yellow right eye and a purple gemstone in the left eye and a frilled neck and has a cybernetic left arm and spikes jutting out from his shoulders and wore a dark grayish-blue pants, brown belt, black boots and a purple cloak that cover his right arm.

"When Seth suggests you, bounty hunter, I was concerned, but I see why Seth recommended you, the Chaos Emerald you got from the Monster Temple has arrive safely."
"I aim to please" said Rasticore.
"For now, Rasticore, stay put there and if anyone find out about our takeover of Monster Temple, dispose of them." commanded Seth.

"As you wish Lord Seth" then the transmission ended as the hologram table automatically turned off. Then Seth turns to Eggman and asked, "any progress on the wand doctor?"

"Surprisingly despite the energy from the Master Emerald, it will take several hours before the wand is fully restored. If we want to speed it up, we need to gather the remaining Chaos Emeralds."
"And your Death Egg Robot modifications?"
"At 50%, with the modifications, the Emeralds and the wand, my Death Egg Robot will be indestructible and soon will be my robot army."

"Good" answered Seth as he steps aside and whispered to himself "and soon I won't need that egghead fool anymore."

Meanwhile in Echo Creek, we find Star completing her story to Sonic and his friends as they reach Janna's house.
"And that's how New Mewni was created and that was 3 weeks ago."

"Wow Star, you, your friends and family must have been through a lot since?" Asked Sonic running alongside Star as she replied.
"Yep, we been keeping the peace while having a normal life, those Solarians lead by Mina Loveberry are still around but not causing a major problem since I destroy the Realm of Magic, but then these rumors of this Septarian army looking for magical emeralds began and the rest you know."

"I'm surprise this Realm of Magic of yours doesn't have a guardian" said Knuckles as Marco walk up to the front and ring the doorbell. "From what you told us Star Butterfly, this Realm of Magic sounds dangerous just by someone having amnesia and memory loss while in that realm, I know magic can be powerful, but magic shouldn't erase someone's memory on its own."

"You know Knuckles, you make a fair point..." but before Star could finish, Janna opened the door to meet her friends, she has short dark-blue hair, brown eyes and wore an olive-green shirt, turquoise jacket, yellow skirt, brown boots and an olive-green beanie hat.

"Where are your alien friends?" she asked Marco then Sonic dash besides him and raise his right arm for a handshake and said, "Sonic the Hedgehog is my name and speed is my game."
"Whoa cool, Janna Ordonia and I can tell we are already going to get good friends." Janna introduces her as she gave the blue hedgehog a handshake. Then she show her friends into her home and to the living room and then said as she closes the door "you need to tell me everything."

Sonic and his friends explain to Star and her friends a little more about their selves, Mobius, the Master Emerald and the 7 Chaos Emeralds, and about Dr. Eggman along with the recent event at Angel Island which lead them to Star's world.

"So, let me get this straight" began Janna as she holds a yellow Chaos Emerald in her hand that she brought down from her room, "these 7 Chaos Emeralds has the ability to turn thoughts into power and this Eggman guy tried to use these Emeralds along with the Master Emerald which control all 7 Emeralds at once to take over your world, but you and your friends defeat him every time, and recently he team up with the Septarian and stolen the Echidna's Master Emerald and you believe he and the Septarian plan to use it to find 5 remaining Emeralds, which somehow ended up on our world, and use the Emeralds to create some kind of super weapon to be use to take over both worlds?"

"Pretty much."
"Cool, classic good vs evil and stuff."

"But there one thing I don't understand, why would this Septarian want to do this?" asked Tails which Star replied "because the Septarian hate my people, the mewmans, the humans that live on Mewni before the fusion. They hold a centuries old grudge against my people and my family back when we were royal and have magic. In fact, centuries ago my kind used to view monsters, as nothing but wild beast and took a lot of their land. In fact, at once point in my family history, Solaria Butterfly started a war against the monsters of Mewni which make the Septarian hate mewmans even more."

"The very same Solaria that created the first Solarian Warriors and Mina Loveberry?" asked Knuckles siting on the couch alongside with Janna.
"The very same." answered Janan.

"After what you told us about your world Star, now it makes perfect sense, these rumors began a week after New Mewni was formed which at some point they discovered how to use a Chaos Emerald to reach Mobius, make contact with Eggman and team up." Tails explain " but we still don't know about their lead named Seth who we only hear about once on Angle Island."

The word 'Seth' hit in Star's mind and then remembered somethings and asked, "Did you just say Seth?"
"Yes?" answered Tails with a concern look on his face.

"Yes, I remember now" yelled Star as she ran upstairs to Janna's room and said, "I'll be back, I need to get the Book of Spells."

"Book of Spells, I thought, she can't use magic anymore." asked Sonic which Marco replied, "yes but her Book of Spells is also a family history book, and since destroying the Realm of Magic, Star gave it to Janna for safekeeping and to allow Janna to read about Star's family past."

"Did you know that the Book of Spell that Star has only have info about 27th to up to Star's chapter? The original Book of Spells was destroyed in a fire when Skywynne was crowned Queen of Mewni, in fact Skywynne create a new Book of Spell which is in my room."

Then Star came back downstairs carrying a large heavy old book with its front cover having 2 gemstones at the center of an upside-down infinity symbol which look like an '8'. Star walk up to the living room table and place the heavy book down, open the book and started turning pages to Eclipsa's chapter at entry 270 which has a wanted poster with Seth's name on it taped to the back of the page which show a picture of the Septarian in question.

"I knew I know that name before, this Seth guy was mentioned a few times in this book starting with this chapter which Eclipsa explain that one particular faction in the monsters of Septarsis which could be the homeland of the Septarian Warriors, only wanting the total destruction of the mewmans and magic, not peace." then Star turn the page to Crescenta's chapter which mentioned Seth a few times in "Era of the Bunnies, Year 8, 9, and 10", then turn to Estrella's chapter which show a comic of the Magic High Commission members talking about Seth leading a small group of rebels and finally reach her grandmother's chapter, Comet Butterfly.

"Whoa Star, your family have unique history with Seth." said Tails as he reading the chapter pages along with Star which she replied "and more. Comet's chapter was the last one mentions Seth and his Septarian army. She mentions him as a dried-up, old gecko and despite her conviction that Seth's position is an old, decaying one, she has concern about Toffee, Seth's 2nd in command, and that when Seth disappeared, Toffee...well..."kicked my grandma's bucket" and her chapter ends and my mom defeat Toffee and then he disappeared until I encounter with him and the rest I told you on the way here."

"Do you think Seth has returned and still alive?" asked Marco which Star answered "I guess so, which could explain the Septarian army being gathering back together and now team up with Eggman. From what I read about him with the little information in this book, Seth is basically a Septarian version of Mina Loveberry."

But before someone could speak, they heard a loud knock at the front door, then Janna got up and walk towards door as she said, "I'll get it, who could that be?"
Then she opened the door met with a large, pale green humanoid frog with a bulky upper body with disproportionately legs, yellow eyes, dark-green lips, small, webbed wings on each side of his head and wore a light green tunic and a gray belt with a skull buckle.

"Oh, hey Buff Frog, what's bring you here?"
Buff Frog is a former enemy of Star turned allied and friend. The frog monster look wore out as if he was running all day and his tunic look torn up as if he was in a fight.
"Where is Star?" he spoke with a foreign accent and a worried look on his face with sweat dripping down his head. "I need to tell her."

"She just got here dude but we're in a middle of something."
"It's about Moon"
"She's in the living room." answered Janna as she steps aside and pointed towards the living room as Buff Frog rush into the house, thanking Janna, and find Star and Her friends siting in the living room.

"Buff Frog? Why are you doing here and what happened to you?" ask Star as she noticed Buff Frogs worried look and torn up tunic as Buff Frog tried to catch his breath and then said, "Septarian has taken over Monster Temple with robots."

"What?!" Star, Marco, and Janna yelled as Buff Frog explain, "Me and my children were visit Moon and River since they're house siting for Eclipsa and Globgor while they're away. Then Rasticore lead a Septarian squad and use robots to captured temple staff including your parents and my children. Only I managed to escape."

Sonic handed a bottle of water to Buff Frog as the frog monster sit on the other couch besides the one Knuckles and Janna are siting.
'Thank you, blue hedgehog boy, I needed that" said Buff Frog as he opened the bottle and drink the water inside. "I don't believe we met before, Yvgeny Bulgoyubov, but I also go by Buff Frog, and you are?"
"Sonic the Hedgehog, The Fastest Thing Alive and expert of destroying evil robots."
"Buff Frog, you said my mom and dad got captured by Rasticore?!"
"Yes Star, but before I managed to escape, I overheard them talking about a Chaos Emeralds from those rumors." but then Buff Frog, wore out from running to find Star all the way from Monster Temple, pass out on the couch and fell asleep siting. Janna checked on Buff Frog said, "don't worry guys, he just unconscious, better let him rest for a while."

"OMG, my parents and Buff Frog's kids are in trouble."
"Don't worry Star, we'll save them." Said Marco as he walks up besides Star and put his hand on her shoulder to comfort her.

"Yeah" cut in Sonic, "and we're going to help out, these must belong to Eggman and this Rasticore guy must know something about Eggman and Seth's goal."
"And the location of the Master Emerald" added Knuckles.
"Thanks guys" said Star then she turned to Janna and said, "you should stay here and watch Buff Frog in case he wakes up."

"Sure thing." said Janna although in her mind she's actually disappointed that she is not going and have to sit on the sidelines, but she also know that someone got to stay here and watch Buff Frog and possible warn someone about what's happening that Monster Temple in case Star and her friends need back up. But then decided to give her yellow Chaos Emerald to Star, knowing somehow her friends could need the Chaos Emeralds when the time is right.

"Here Star, something tells me you guys need this before the day is done."
Star thanks Janna and place the yellow emerald in her bag with white emerald as she suddenly felt an odd, but familiar feeling as if she felt that feeling before. But her mind went back to the current situation as our heroes ran back out to the front yard as she and Marco hop back on their bikes and head towards the direction of Monster Temple with Sonic and his friends following them to help their new friends on a rescue mission.

Meanwhile back at Neo Scrap Brain Zone in the Central Complex Building, Seth step into the command room and making sure no one is watching him and that he's all alone. Then began typing in the main computer for look for more info about Sonic and about the Master Emerald and the 7 Chaos Emeralds and began reading about Eggman's past encounters with Sonic and his friends, Eggman's past schemes, unused designs and plans and dead-end research until finally he found Eggman's research on the Chaos Emeralds that Eggman gathered over the years.

Research notes on the Chaos Emeralds and Master Emerald energy, research about ancient stuff circling around the Emeralds, the Knuckles clan, Angel Island, Tikal and Chaos, theories, tests and experiments. Until he reaches a whole lot of info about Super Sonic and his super form. This super form only appears when Sonic use all 7 Chaos Emeralds combined and absorb the emeralds their selves which change Sonic from a blue hedgehog to a very powerful, almost invincible golden-yellow hedgehog. As Seth read more about it, he came across information about Mecha Sonic, one of Eggman old robots based on Sonic and learn that Mecha Sonic is the only one robot can absorb the energy of the Master Emerald but unlike Sonic, Mecha's super form didn't last long due to bring a robot and was eventually defeated by Knuckles.

"This is exactly what I been looking for" said Seth to himself as continue to read the info for his own research.

Note: Star vs the Forces of Evil belong to Disney and Sonic belong to Sega, I don't own anything. This is my very first fanfiction story so my writing will not be perfect. I hope you like this chapter now that I'm getting a little used to this, but still need improvement. Also, if you're wondering "where the heck is Marco's parents, Tom and etc.?" Well Marco's parents went on a vacation which was a gift from Star and Marco for their anniversary, and they won't be in the story. Same goes with Tom, he borrowed Nachos, Marco's Dragon-cycle for a cross country adventure. Don't worry, Pony Head is later in the story.