A/N: It's been a long time since I've written anything, so I'm not making any promises. Also, this ignores the fact that Yang has already gotten to Haven.
Disclaimer: I own nothing.
After all this time, they had finally made it to the doorstep of Haven Academy. The school had been turned into a fortress after the Grimm started invading. It was the last safe place in Mistral. "Heh, looks like this is my stop, Blondie." Mercury said, a half-smirk adding some life to his disheveled appearance. His hair was a mess, he had holes in his clothes, he was missing his right armguard and his aura had broken ages ago, but they had made it.
His travel companion was not much better. There were a few cuts and tears strewn out sporadically around her outfit, her golden prosthetic arm was in need of a new paintjob, her aura had broken before they had gotten within the boundaries of the city, and her lilac eyes lacked their usual ferocity, showing just how draining the trip was.
The blonde fighter looked past him to the hellscape of an environment around them. The skies were bloody red with clouds of pitch black swirling through it. The clouds cast shadows onto the land, giving everything a darker, edgier tone. All around were crumbled remains of what just last week had been a student hangout. Now, little more than debris remained standing, but that didn't mean anything to the Grimm, who continued to roam on and look for people to attack.
"You know, you can come in, if you want." Yang said, making herself look anywhere except for at him. A week ago, when the calamity struck, Yang begrudgingly let him come with her, but she made sure he knew that he wasn't allowed in – not after all he did, after all he put her through. She couldn't see it, but she knew his smirk had gotten bigger.
"Aw, we haven't even left each other yet, and you already miss me." Mercury said, teasingly.
"I'm being serious, you jerk!" Yang said, locking eyes with him, some ferocity returning to hers.
"I'm touched," Mercury said with a chuckle. Movement could be heard just beyond the entryway. It wouldn't be long before the welcoming committee made their way out there. "But I'm going to pass."
"Why?" Yang said. Her face contorted in confusion, eyebrows furrowing.
"After all I've done, do you have to ask?" Mercury said, casting another glance up and down the academy. From where he stood, he could see the great stone doors of the academy slowly opening.
"That doesn't matter, now. You're trying to change, you said so yourself!" Yang said, protesting. A week ago, she would not have cared what happened to him, but it had been a long week and a lot had happened. "At least, come in to rest up and get supplies."
Yang could see the gears turning in his head, debating on what to do. After a few moments, it looked like he had finally come to a conclusion. His mouth opened and then –
"YANG!" The scent of roses washed over her as she was suddenly tackled to the ground by her loving little sister. "You're okay!" She sounded like the embodiment of joy and happiness.
"Hey, sis." Yang said, laughing and giving her a once over. She had grown since Yang last saw her. "You haven't gotten into too much trouble without me, right?"
"Mmmaaaayyyyybbee." Ruby said, a cheeky little grin lighting up her face. Yang patted her on the head and pulled her in for a hug.
"I missed you, Rubes." Yang said with a smile, before she started squeezing Ruby tighter and tighter. "But you're in trouble for running off like that."
"Aaauugh, I'm sorry, I'm sorry!" Ruby said, her eyes practically popping out of her head. Yang gave it a minute more before she released her and started laughing. "That wasn't funny, Yang." Ruby huffed.
After a couple moments, Yang just laid there on the ground, her radiant smile finally returning. Her sister was safe and they had been reunited. And everything seemed a bit less intimidating.
"So, who were you talking to out here?" Ruby said, looking around. "You didn't go crazy while I was gone did you?"
"No!" Yang said, "I was talking to Mercury, he's right over…" No one else was there. She sat up, pulling Ruby up with her. "Where'd he go?"
In the distance, the guttural roars of Grimm could be heard. "We should probably head inside now." Ruby said, hesitantly. "Everyone's going to be happy to see you."
Explanation: The idea is kind of half-baked and set in an AU where Haven has already fallen and, unlike Beacon, they haven't managed to run out the Grimm, yet. It also ignores that Yang has already arrived in Haven. Instead, Mercury kind of left the villains crew after the collapse of Haven and started wandering around, where he eventually bumped into Yang. They fought, talked, and then Mercury decided that he would also take Yang to Haven Academy because he didn't have anything else to do. And maybe or maybe not because he felt a bit of guilt. This is all set at the end of that voyage. I'll consider writing the earlier events at a later point of time.