Crossberry but they meet at a masquerade ball. Cross is there doing some spying for nightmare and Blueberry is there because he's kind of a big deal. Blue has never seen Cross before so he doesn't recognize Cross through his outfit. Cross doesn't recognize Blue because blue went all out on his costume and is really well hidden. They meet by the snack table and both start munching on the tacos. They strike up a conversation due to their mutual love for the food. They start having a great conversation because Blue is actually pretty cool and not childish and Cross treats Blue like an equal. They head out onto the balcony to keep talking. Cross eventually compliments the tacos he's eating and Blue reveals that he cooked them. Cross realizes "Shoot! I've been talking to underswap this whole time. Double shoot! I had a really nice time." He panics and tries to leave but Blue doesn't let him until Cross agrees to meet him again. So the two make arrangements to meet in outertale. Cross's only request was that they stayed in masks. So the two meet up a lot in the months that follow and Cross realizes that he's starting to have a crush on Blue, who actually acts differently than everyone else expects him to. Cross doesn't see Blue like that anymore because he didn't have that bias when he first met him.
But they meet on the battlefield one day. Each skeleton from the Bad Sanses is paired off against someone from the Star Sanses. Ink against error, Dream against Killer and Blue against Cross. They all start fighting but Cross gets distracted by Blue's determination. He can't fight right because he knows who it is. He starts purposely missing. Then, blue almost gets him but Killer hurts blue before Blue could get to Cross. Instead of thanking Killer like Killer thought he would do, Cross freaks and teleports blue to outertale. Where he slowly nurses blue back to health
Cross reveals who he was and Blue is like "lmao I knew all along."
They decide to team up and form their own group for a little while. They start hanging with the Star Sanses and their groups kind of merge.
The rest of the story is just cross learning to be a good guy.
Oh and a year later or something, Cross confessed his love and vows to always fight at Blue’s side.
Blue is just like “LOL I already knew that babe. Now kiss me like a man.”