Demon moons were an odd phenomenon on Mewni. The mystical heavenly body wasn't the same as the Blood Moon-which showed up only once every 667 years-but was rather a lesser moon that rose from seemingly nowhere and bathed the night sky in sickly light at least one week a month. Sometimes it appeared several times, depending on how long or short Mewni's odd months were.

As a result, the supernatural moon inspired many old wives' tales about its origins and purpose. Some said the moon rose from the Underworld itself, opening a portal to allow hungry demons to prowl around and kidnap naughty children to eat. Others said it had the power to change Mewmans into savage monsters. Still, some said the moon was a harbinger of anything from a plentiful corn harvest to defeat in warfare.

Naturally, Marco Diaz didn't believe in the old legends when he first came to Mewni, no matter how convinced the citizens of the kingdom were of their beliefs. Mewmans tended to be a superstitious bunch. They spent gobs of money on charms to ward off evil, believed talking calzones could predict how one would die, and practiced ritualistic blood sacrifices to appease an evil Stump god. In fact, just the other day, Star confessed no one ever celebrated her birthday on the actual day because of the tree deity. Being a good boyfriend, Marco tried not to laugh at how terrified Star was over a dead tree. It seemed ridiculous!

However, it was during the silent nights when the red moon's light filtered through Marco's window that the tales of demons and monsters clung in the back of his mind. Perhaps feeling heavy horns weigh on his head and his tail thrash under the covers helped make the stories real. Now, he knew better. The legend of the demon moon wasn't just old wives tales.

It was two in the morning and Marco was wide awake, his soul buzzing with a strange energy that forbade him from getting rest. He tried everything in his power to relax—drinking hot tea, practicing Tai Chi, reading a few books—but nothing worked. Groaning, he shoved his pillow over his face and tried to block out the taunting glare of the demon moon. This is your life now, Marco Diaz, it seemed to snarl. Rise up and walk the night!

No! Marco's tail twitched beside him. Responsible young squires went to bed on time and woke up bright and early! Staying out all night was bad for physical and mental health. He might be part-demon now, but he wasn't going to jeopardize his wellbeing to satisfy base urges.

Either from the lack of fresh oxygen or he eventual tiredness, Marco felt his eyelids droop as the black of Dreamland crept across his vision. Sleep...he purred to soothe himself, the rumbling forming a gentle lullaby.

That is until the door of his bedroom slammed open. He flung himself out of bed and landed in a crouch on all fours with his tail high and back arched. An intruder! But he relaxed when he saw that it was only Star. Purply-pink light from her wand illuminated the room and her face, which was full of energy and spirit despite it being so late in the night.

"Can you knock next time, Star?" Marco eased out of his crouch, feeling embarrassed. "I'm kinda not decent..." One of the many downsides to having a demon form was constantly being hot. Naturally, sleeping under covers made things worse, which meant his usual flannel pajamas were out of the question. During demon moons, Marco slept only in his boxers, and he wasn't ready for his girlfriend to see this much of him yet. He was still working on the abs.

"Oh..." Star's cheekmarks lit up a deep, lusty red and she chewed on her wand. This went on for several long moments.

Marco cleared his throat, "Star...everything okay?"

"Huh? Oh, right!" She got herself back on track. "Guess what time it is?"

"Time to sleep."

"Wrong, Diaz," she waved her wand and covered his body in his clothes. "We're going to practice spell casting! You promised we would the next demon moon, and here we are!"

He wanted to tell her no, but how could he reject the energetic gleam in her eyes and the wide smile on her face? It was impossible! Resigning himself to another sleepless night, Marco sighed and stood up, "Fine. We'll do some training."

The second he finished speaking, his girlfriend eagerly grabbed his hand and yanked the poor demon out of his room. On the bright side, spending time with Star was always something to look forward to, and he couldn't wait to see what he could really do with his demon powers. Reading books and talking to Tom could only do so much.

Outside, in one of the castle's courtyards, the two teens stood under a beautiful night sky studded by a million colorful stars and lit up by multiple moons, including the ominous red one. Wow... the sight took his breath away. He never saw a sky like this back in Echo Creek. But, of course, the most beautiful star of all stood right beside him. His bright and shining Star.... His bright and shining Star who yelled, "NARWHAL BLAST!" at the top of her lungs and sent horrified, horned, blubbery sea mammals careening towards his face.

Crap! Marco just barely managed to dodge the attack, rolling out of the way and onto his feet to face his opponent. Right. He remembered Star showed no mercy in combat, and he had to purge his mind of warm feelings during training. So far, he had perfected basic fire magic, which Tom said was something babies learned before they could walk. At the same time, he didn't want to actually hurt Star in a training exercise with random experimentation.

Suddenly, a rainbow fist smacked him upside the head and sent him into a bush along the edge of the field. Star's laughter fixed the air and her eyes blazed like bright comets against the backdrop of the night sky. She stood over Marco, cracking her knuckles and gripping the shaft of her wand with confidence, "Eyes on the prize, Diaz!"

She took a pace forward and summoned another Narwhal Blast, but Marco was ready this time. He made a fiery shield and raised it up to block before chucking a surprise fireball at Star with his right hand. It singed part of her hair as she evaded, but the princess wasn't afraid. In fact, the brush with danger made her more determined to beat him.

"I guess you need to keep your eyes on the prize, Butterfly!" Marco teased. "I'm just getting warmed up!" And literally too. He could feel his magic reserves filling to the brim with crackling and sizzling fire as he became more and more energized by the demon moon.

He curled his lip in a cocky grin as he flicked a red fireball after fireball in an endless torrent that lit up the night in mini explosions. However, Star dodged each one and answered his fire with magical blasts of her own. When the two of them fought, it was like dancing. Full of fury and passion with each anticipating the other's moves like if they were their own. It was personal—almost intimate—because nothing was better than gloating over being better.

After many moments of intense magical dogfighting, Marco had to take a breather. Stamina was something he was still working towards. Meanwhile, Star was rearing to go, "I wanna see you hit me with your best spell, Marco."

The demon geared up for part two of the training session and met her challenge with one of his, "Then gimme yours, Star! You're going easy on me."

An evil grin formed on her face as she twirled her wand in her hand. Uh oh, he knew exactly what her weird magic,anime-girl dance meant. Warnicorn Stampede. He had to think of something and stat! Spell creation was Star's specialty; she had a bizarre knack at spewing random words and having it turn into spells that worked. Or didn't. Perhaps, Marco had to dig deep and do the same. What could counter giant war unicorns? How about even more warhorses? Marco's mind lit up. It sounded totally unoriginal, but it could work. Also, it better because Star was about to unleash her wrath. Now, how to summon what he wanted....

He pounded the ground, feeling the legions of the Underworld waiting to unleash his will upon them. "Ultimate Skeleton Army Stampede!" The phrase clunkily rolled off of his tongue, but the ground rumbled in obedience, releasing an army of flaming deadhorses. The warnicorns collided with the skeleton beasts and the spells offset, blasting their wielders far apart in a bright red blast.

When Marco came to, he was dangling from a tree branch high above the ground, gazing down at a totally destroyed field. All of the grass had been burned away and flowers killed. Oops, he chuckled. Good thing they didn't practice in the Rose Garden or Eclipsa would have killed them.

"That was AWESOME!" Star cheered as she rose off the scorched ground. "You did it, Marco! You cast a real spell! Uh...Marco? Where are you?"

"Up here!" He called to her from his perch. The vibrations caused the branch to snap, sending the screaming Marco Diaz into his girlfriend's waiting arms. She held him bridal style and stroked his hair until he started purring gently.

"So cute," she kissed his forehead, making the purring even louder. "Anything else you want to do tonight?"

"Sleep," he yawned. Maybe this was what he needed—a good three-in-the-morning fighting session.

"I'll join you," Star carried him to his room.

"Like in m-my room?!"

"Duh, it's called a sleepover," she said matter-of-factly when they reached his room. "Plus, it's Relationship Thursday, why not get an early start?" Before he could argue implications of having a girl spend a night with him, Star had curled up next to him and fallen asleep with her head on his chest. I guess magic isn't the only spell she has on me, he smiled and held her close as he fell asleep.