If Marshall's heart was still beating, it would've been going like never before. One of the benefits of being undead, he supposed. It was much harder for your body to give away your intentions. Though it still gave away plenty in front of Fionna. He smirked as her image rose up in his mind. She gave away even more, innocent little thing. But if he got his way, then that might change.
Oh, she'd still be innocent compared to him. But not like she was now. All he needed was.. permission? Nah, more like begrudging acceptance from her psychotically protective cat. But maybe she'd be a little less strict seeing as it was Fionna's birthday tomorrow and everything. He was her boyfriend, after all. Kitty couldn't exactly expect him to wait until he put a ring on it, if Fionna ever let it go that far. His feelings for her weren't an issue in that respect, as they were never going to change. Not after everything that had happened.
Speaking of which, it wasn't like he had to lay down all his plans for Cake. Nothing wrong with a little bribery and corruption every now and then, hm?

Marshall-lee drifted into the treehouse without checking to see if Fionna happened to be around. He knew she was in the Candy Kingdom, as she had called him to break a demon hunt to go help out Gumbutt. Talk about cock-blocking. Just because Bunny had chosen a king over a prince.
He could hear Cake yelling at Beemo- or rather, the ' lousy, gronked-up' game that Beemo was playing her- and floated lazily into the lounge, smirking at the cat's puffed out tail and bared fangs.
' Cakey, stop yelling at Beemo, she's not making you bad at video games.' Cake turned around and hissed at him dramatically.
' You shut your pie-hole, Marshall! Just 'cause y- Wait, what're you doin' here? You know Fionna's helping out Prince Gumball with his sunshine thingy.' Marshall-lee nodded condescendingly.
'Yeah, Fi broke a date for him. I feel kinda betrayed. But I came here to talk to you, Cakers.' At this, Cake glanced worriedly at Marshall-lee before quitting her game and shooing Beemo then swiveled around, supiciously giving the vampire her full attention.
' I ain't liking the sound of that. What do ya need me for?' Somewhat gratified by her reaction, Marshall-lee stretched his mind, psyching himself up. This would be an nice challenge.
' I wanna do you a deal about Fi's birthday tomorrow.' Cake raised an eyebrow, her interest piqued.
' I'm listening.'

' You can have Fionna all day, no interference from me. Do whatever you want, I won't try and butt in. Sound good?' Cake nodded, eyes narrowed as she folded her arms.
' Yeah, does sound good. But what's in it for you? Don't give me BS about the goodness of your heart either, I know you.'
' Do you?' Marshall-lee replied, and smirked unrepentantly at the look he got in return. He paused for a second, trying to think how to phrase his request as such that Cake would give him what he wanted without neutering him into the bargain.
' So you've got Fionna for the day, so I want her for the night. It's better for me because, obviously, I'm a vampire. I can take her anywhere at night without having to worry about either of us.' Cake twirled her whiskers, considering it. That seemed like a reasonable request.
' Yeah, I'm cool with that. What time will you be bringing her home?' Marshall-lee immediately jumped into gear, trying to formulate a suitable excuse. Having her for the whole night was the best possible outcome... Yeah, all night long.
' I actually want to take her to a place I know and show her the stars. There's a particular constellation that's only visible there at about three am though. Figured I'd just bring her sleeping bag along and she could crash there and I'd bring her back in the morning.' Marshall-lee said casually, crossing his fingers behind his back.
Please buy it, Kitty!
He pulled his best ' I'm serious' face as Cake scratched her chin, eying him with trepidation.
'... All right. Besides, if I said no, you'd get all butthurt and then so would Fionna because you two have like some weird mind-meld with your emotions.' Marshall-lee shrugged, mentally pumping his fist in triumph.
' Eh, we're in sync. Kinda happens, especially what with the whole Lich episode.' Cake conceded, going to sit down on the couch and waving Beemo back over to her.
' Yeah. If that's it, them Imma go back to owning this schizz.' Cake said determinedly, picking up the controller. Marshall-lee admired how confidently she hid her apprehensiveness.
' Ha. "Owning." If that's what you wanna call it...'
' Get out of here, you jerk!' Cake replied angrily, tossing an empty soda can at the vampire in annoyance. Marshall-lee dodged it easily and floated out of a window, laughing to himself.

As soon as he was outside, parasol and all, he joyfully flew up into the sky and flipped over a few times, barely resisting the urge to yell out. He knew his Bunny-baby would be into it, or at least he was pretty sure. Fionna was a bit of an enigma when it came to romance, seeing as she only knew the logistics of it. But banking on the fact that she loved him? Tomorrow night would be the best night of his life... Well, death.

' Hey Fionna, so what was wrong with Gumball's sunshine thing?' Cake asked as Fionna appeared up the ladder and collapsed next to her cat on the couch, blowing up her fringe.
' Eh, he just needed a test subject. I was like, crazy happy on that sunshine juice, sis. It' s like catnip for people.' Cake laughed and draped herself across Fionna's lap.
' I wish I'd seen that.' Fionna giggled with her. ' Yeah, it was pretty funny. But I'm real tired, so I'mma go to bed now.' She said, standing up and stretching. Cake wrapped her arms around Fionna's midsection and stretched them both up to their room at the top of the treehouse.
' Okay, sugar. You sleep tight now, you've got a big day ahead of you tomorrow.' Fionna grinned at her, remembering what she was referencing.
' Yeah, I do! Night, Cake.' Cake waved to her affectionately before disappearing back down the ladder. Fionna quickly changed into her pajamas and hopped into her sleeping bag, snuggling down under the furs. Her sixteenth birthday was gonna be awesome! Not to mention it'd also be her first birthday with a boyfriend. She smiled, thinking of her vampire lover singing a rather sassy rendition of 'Happy Birthday.' That'd just make her day.

' Whatcha thinking about, baby?' Fionna jumped at the sound of his voice and looked over her shoulder to see Marshall-lee lying behind her on top of the covers, his head propped up on one hand. After recovering from the initial shock, she smiled and allowed him to snake his free arm around her waist and pull her in to him.
' I was thinking about what you'd do for my birthday, actually.' She whispered. Marshall-lee smirked behind her head where she couldn't see. He knew exactly what- or rather, who- he was doing for her birthday. Aw yeah.
' Mm, I've already fixed something up with Cake. So I won't be here when you wake up, and then I won't see you again 'till tomorrow night, But then I'll have you all to myself.' He said, kissing the back of her neck. Marshall could tell that Fionna was surprised by this information, despite the fact that he couldn't see her face. Wow, Cake was right. They really did have some sort of weird emotional mind-meld.
'How'd you get Cake to agree to that? She only lets me go on dates with you if we're like, going dungeon crawling or something.' Marshall-lee shrugged, not really caring. Fionna smelt like coffee and that undefinable, addictive smell that girls always have. It was very distracting.
' Eh, I have my ways. Go to sleep, sweetheart.' Fionna snuggled in closer to him and Marshall-lee hummed soothingly in her ear as she drifted off into her dreams.