"This isn't fair, you know!" Supergirl huffed as Nathan Garcia, aka Cosmic Spiderman, prepared to paint her stomach. She crossed her arms, obviously annoyed yet trying not to smile.

"Rules are rules, Supergirl," Nathan countered, his voice a mixture of amusement and sympathy. "You lost the bet, remember?" They had had a spirited competition, which Supergirl had lost.

Our friendly neighborhood Spiderman turned cosmic superhero had a charming smile, which flustered Supergirl momentarily, she considered him cute and occasionally called him sweetheart.

"Alright, sweetheart," she sighed, rolling her eyes playfully. "Just remember, I'm only letting you do this because it's you." Nathan chuckled. His blush was as bright as his superhero suit.

Nathan picked up a paintbrush, his hand shaking slightly under Supergirl's watchful gaze. His heart fluttered. He was about to paint the belly of a superheroine, and not just any -- Supergirl!

"Relax, Nathan," she reassured, noticing his nervousness. "I won't burn you with my heat vision," she joked. Supergirl's attempt to lighten the mood worked as Nathan cracked a smile.

He dipped the paintbrush into the pot of bright green paint. Nathan had decided to paint a spider web, a nod to his superhero identity. He touched the brush to her belly, starting his work.

Supergirl flinched at the cold touch of paint against her skin. She had to admit, it tickled a little. She laughed, causing Nathan to glance up in surprise. His face flushed redder, if that was possible.

"Sorry," she giggled, trying to stay still. The sight of a blushing Spiderman was simply too amusing. He was usually so confident, but this situation had turned the tables amusingly.

Nathan smiled at her laughter. It was a rare sight to see Supergirl so informal, so carefree. He continued his work, lines of green starting to form the pattern of a spider web.

As he continued painting, Supergirl felt strangely at ease. This was definitely a departure from their usual high-stakes battles and world-saving missions. It felt...nice.

Nathan kept adding details, carefully painting each strand of the spider web. He focused on every stroke, lost in concentration. The green paint against her skin began to take shape.

Supergirl watched him, her initial annoyance turned into fascination. There was an unexpected gentleness in how he moved, something she hadn't noticed in their battles.

As the pattern of the web completed, Nathan picked up the black paint. He was going to paint a small spider crawling on the web. It was a task requiring precision, and he was up to the challenge.

His hand began moving carefully, creating the outline of a small spider. "This is actually fun," he admitted, giving her an embarrassed grin. Supergirl chuckled in response, enjoying the unexpected fun.

Soon, Nathan finished painting the spider. The end product was a sight to behold. The spider web on Supergirl's belly was an artistic depiction of Spiderman's identity, with Supergirl as his canvas.

Both superheroes took a moment, looking at the finished piece. It was a symbol of their friendship and mutual respect, painted on the belly of one of the most iconic superheroes.

"Well, sweetheart, you're definitely a better painter than I expected," Supergirl said. Nathan reddened, but it was clear he was satisfied with his work. After all, it wasn’t every day you got to paint a superhero’s belly.

As they cleaned up, there was a comfortable silence between them. The afternoon had turned into an unexpected bonding session, bringing two superheroes closer in a lighthearted way.

Nathan promised to uphold his end of the bet, should he lose next time. Maybe he'd lose on purpose. He certainly wouldn’t mind if Supergirl painted his belly. Especially if it meant seeing her laugh again.

Supergirl grinned at the thought, a mischievous glint in her eyes. She didn’t plan on losing next time. But the idea of painting Spiderman's belly did sound entertaining...

So, as the sun started to set, they shook hands and agreed to another competition. After all, it wasn’t about winning or losing. It was about the fun and bond they shared — even superheroes need downtime.

As they parted ways, Supergirl looked down at the spider web painted on her belly. A smile spread across her face. After the day they had, she decided she might keep the painting for a little while longer.

Nathan, on the other hand, felt a sense of accomplishment. He had painted Supergirl's belly and more importantly, made a friend. He knew their friendship was just beginning to deepen.

And so, another day in the lives of two superheroes came to an end. As they each returned to their solo missions, they each carried with them a piece of the other – a memory, a painting, and a strong bond.