To Error, Fresh was an enigma. An annoying enigma, but still. Whatever he was, he clearly wasn't a Sans, and he had no home universe as far as Error could tell. All he was was a parasite. A virus that needed to be eradicated. An emotionless creature that would puppeteer the lives of others and derived pleasure from hurting people. And that angered Error. After all, he was the only one that could do that.
To Fresh, Error was interesting. And fun to mess around with. He enjoyed trying to find the other's weaknesses and exploiting them. And he loved to see the anger on Error's face every time he saw Fresh. Error wasn't the coolest of dudes, but he was just as much of an enigma. And Fresh really wanted to figure him out.
Blueberry was just caught up in this whole mess. He had no idea what was going on 90% of the time and honestly, he just wanted to go home to his brother. Error and Fresh were both his friends, of course! But they were both a little...murdery...
...And they hated each other. It seemed like every time Fresh showed up in the anti-void, Error would immediately become protective. Almost more so than Papyrus was... And Fresh would start annoying Error as soon as he showed up. Teasing him and trying to guilt trip him about things... It always just made Error more mad. And soon enough, it devolved into petty insults and fighting with Blueberry watching boredly on the sidelines
"Can you two please stop?" He suggested after watching their argument for a few more moments.
Error turned to face him, his eyes narrowed as glitches flew frantically around him. "Of course not! This abomination shouldn't even exist! I don't even know why you like him... He's a parasite! And his clothing choice is really lame."
"Yo, don't diss my threads, man." Fresh commented with a frown.
Blueberry rolled his blue pupils. "I told you! He's cool. And nice. A lot nicer than you are usually..."
Error gasped loudly, offended. "Screw you, I'm a delight!"
"Of course you are." Blue couldn't help but smile a bit. "Can't you two just get along?"
"I'd love to, broseph! Mr. Angst needs more buds anyways. And I wouldn't mind a new friend." Fresh gave Error a grin and a wiggle of his eyebrows.
Error just crossed his arms and looked away. "I don't need any friends. I have tons of friends!"
Fresh didn't look impressed. "Yeah, dude. The version of you you kidnapped after straight up murderizing all his friends, the voices you hear in your noggin, and the dolls you play with all count as friends." He grinned again, adjusting the shades on his face. "'Course, I'd rather not deal with ya either. So no hard feelings."
Blueberry looked away, staring at the floor as Error's eyes narrowed and blue strings appeared in his grasp. "Shut up." Error's voice glitched a bit as he spoke, sounding almost like a broken record. "You don't know what you're talking about..."
Fresh noticed he'd struck a nerve and his grin grew wider. His hands slid into his pockets at he looked up to the ceiling, staring at the countless human souls strung up. "Heh. Yeah, what do I know about friendship? I'm not even a real person, dawg. Then again..." He lowered the glasses from his face, looking straight at Error before giving him a wink. "...who's to say you are either? I mean, it's not like you've got a universe of your own. And your code's so messed up, you're practically an echo of who ya used to be. You're not even worthy of calling yourself a Sans."
"Fresh! Please stop it." Blueberry finally piped up.
"Be quiet, Blue." Error growled. His yellow pupils locked themselves with Fresh's as he took a step forward, his strings dragging on the floor. "I should tear you out of that body right now..."
"Error-!" Blueberry started, but was interrupted by Fresh's dark chuckle.
"Buddy..." His eyesockets were bleeding with purple energy. "I'd like to see ya try." With that, he put his glasses back on and turned to Blueberry with a cheerful smile. "See ya, blueberry bro! I should go ahead and skedaddle." He looked back to Error's enraged face, still grinning. "And I'll see you too, my glitchy pal." Before Error could say anything, Fresh was gone.
"I hate him...so much." Error growled, his fists clenched.
Blueberry just sighed, looking back at where Fresh had dispersed to. He hoped his friends would find a way to get along someday.