After that Day primer: Cinder's virus didn't work, the Battle of Beacon was anti-climatic, classes continued.
At some point this may get a companion piece since I have plot notes for another story/chapter that would cover team RWBY in Atlas up to this and explain some of those fights and conversations alluded to here.

Usual AtD note: I'm publishing the AtD supporting snippets as separate stories since they will be out of sequence and vary considerably in style and content, so best to author follow rather than story if you want to track updates.

Winter strode purposefully into the small cafe, ignoring the cosy decor. Dismissing the nearby patrons and staff with a glance she spotted Weiss at the counter finalising her purchase.
"Weiss"

Her sister turned and smiled. "Winter. You look well"

"As do you, sister. I believe your scar is finally fading"

Weiss ignored the comment "I didn't expect to see you here"

"I should think not." Examining the people around them she could make out what appeared to be several couples... female couples "A student at the Academy said that I might find you here. I understand you wish to speak to me"

"Yes, a personal matter" Weiss picked up her purchases, a pair of miniature strawberry tarts, and motioned Winter towards a rear corner of the premises.

Looking in the direction indicated Winter recognised the back of Ruby's head by her short dark hair; beside her an empty chair. Around the table she also recognised Ruby's sister Yang, and someone she assumed was her partner Blake, but the dark-haired girl had her face hidden against the laughing blonde's neck. It was not the most blatant display Winter had seen since coming inside but it seemed to confirm the rumours of their unnatural relationship. There where also two people she didn't recognise, another 'couple' making a spectacle of themselves - a slender woman with very pale blonde hair with an auburn haired girl unabashedly seated on her lap.

Winter cleared her throat. Once her sister stopped and looked round she started lecturing quietly "Miss Rose is prone to exuberant demonstrations of affection. Frequenting locations such as this, in such company", she glanced significantly at the table, "might lead people to make unwarranted assumptions about your own conduct"

Weiss sighed. "Winter, that is what I wanted to tell you. Ruby and I are together"

Winter leaned closer lowering her voice even more "I know you have enjoyed a close companionship, but I was referring to a more unseemly interaction. Despite the fact that you are both women, there may be an implication of-"

"Winter," Weiss cut her sister off urgently, "I know about homosexuality. I'm dating Ruby"

"I see. I hope you understand that such a label may carry the expectation that-"

"We are intimate," Weiss sighed more heavily, giving up on approaching the issue delicately, "sexually intimate. I initiated it, and we are both quite comfortable with the nature of our relationship"

Winter remained staring at her for a long moment while Weiss held her breath.
"I had no idea that you possessed such inclinations. Does Father know?"

Weiss relaxed "Last week he sent me a first edition of Brun's 'Moral decay and the fall of empires', so I believe so, yes"

"That seems unkind."

"That's Father." Weiss gave a mirthless smile. "Quite valuable, though. I donated it to the Atlas Equality Alliance and sent him the receipt"

"I cannot understand why you persist in provoking him." She pursed her lips, "I take it, then, that you are determined to pursue this infatuation?"

"I am" Weiss nodded firmly

"Then there is no point in me expressing my opinion. We should proceed" Winter gestured towards the table.

Greeting Ruby with a kiss, Weiss placed the tartlets in front of her, then made the introductions.
"Ruby, Yang and Blake you know. Anna, Elsa, this is my sister Winter"

"Hello" Anna greeted the newcomer with cheery smile,
"Hi" Elsa was more subdued.

"Greetings" Winter fixed the couple with a steady unreadable stare.

Anna squirmed under the scrutiny "Uh sorry to dash, but we should be getting back. We promised to meet Kristoff before the next match"

Claiming the vacated chair Winter mused "It's strange, they seemed so much alike. In any other context I would have assumed them to be sisters"

Unnoticed by Winter there was a meaningful glance shared around the table.
"Strange indeed-" Yang started, only to be stopped by a poke in the ribs from Blake.

Ruby cheerfully picked up the conversation "So here we are in Atlas, it doesn't seem like two years"

"Ruby, my sister has informed me of your relationship. She seems quite enamoured with you, perhaps you have hidden virtues"

"Yup, that's me"

"The security for the Festival is very impressive" Blake firmly changed the subject.

"After the last time we chose to take every precaution to guard against undesirable-" As she spoke Winter's eyes moved first to Blake's face, then up and stopped. The silence lengthened ominously. Weiss cleared her throat.

Snapping out of her trance Winter resumed speaking "Miss Belladonna, I was unaware of your... heritage"

"She used to wear a bow" Yang interjected helpfully.

"It is always refreshing to see one of your kind gainfully employed"

Blake placed a restraining hand on Yang's shoulder, answering dryly "Thank you"

"I see that you are not competing in the Tournament. Is this another lifestyle choice?"

Weiss clearly had a prepared answer for this "Ruby and I have been employed as teaching staff at Beacon, it would be inappropriate for us to compete"

"So I heard, most unusual. But for all of Professor Goodwitch's eccentricities I doubt she made the appointment without your cooperation. No matter how impressive your classroom performance, open competition provides a unique learning opportunity, and exposure, even in defeat would be of great assistance to your career."

Yang burst out in Weiss's defence "She kicked the Atlas champs' asses. And today the room was packed with military guys watching their demonstration!"

"Many of our officers are burdened by teaching responsibilities. Admittedly, advanced Aura techniques are a matter of some niche interest. I regret that I was unable to attend, I might have been able to reassure them that she also possesses satisfactory skill with conventional techniques"

"They ran out of Grimm" Yang pointed out weakly, realising that it was a lost cause since Ruby and Weiss seemed disinclined to defend themselves.

"I'm sure it was still very impressive." Winter rose "If there is nothing else, I will take my leave. Miss Belladonna, Miss Xiao Long" she nodded at them, "Ruby, your interest in my sister has clearly become much more than I anticipated. I hope it is not something she will regret" Weiss stood up and moved beside her sister as she continued "Weiss, even if you have no use for my opinion, it is good that you informed me. You have not entirely turned your back on our family"

Weiss put her hand on her sister's arm "Winter, even if we live separate lives, even without lessons or advice, I still care about you. You are my sister"

Unfortunately Yang had seen an opportunity "Yeh, there is absolutely no shame in having a little sister that can kick your butt"

"Yang!" Ruby scolded

"Sis, that is exactly what you told me!" Yang pointed out defensively.

"Sound advice on an unsurprising reversal. I can't see why you would mention it to me." Winter looked at her sister for confirmation. Weiss was looking very uncomfortable. Winter frowned. "Weiss, since you have chosen to abstain from the Tournament, perhaps I should assist with your training. I have no pressing commitments this afternoon, we should duel"

"Winter you don't have to-"

"Please, I insist. We can go to the central training arena at the Academy"

Weiss moistened her lips "It will be very crowded"

"Atlas students respect their superiors, we shouldn't have to wait too long"

Weiss looked to her partner for help. Answering the silent appeal, the younger girl made a suggestion "The south arena is available for visiting staff, it should be private"

"There is no need for an audience" Winter agreed.

Next to delivering a well deserved smackdown, Yang's second favourite thing was watching one "Yesss!" her victory dance was cut short by a gentle slap on the sholder from Blake.

Their footsteps echoed as they arrived at the deserted arena. Yang stepped forward, holding up her scroll "I'll referee"

Ruby looked up from her scroll "Yang," she pointed at the main display where Weiss and Winter's names and Aura levels were already displayed, "staff access, we can use the main system"

"You are totally milking that gig"

Winter cut their banter short to lay out the rules "Single bout, traditional duelling rules-"

Weiss interrupted "Training limit"

Winter reiterated "Traditional. It isn't as if you have to be ready to compete later. Real fights don't just stop at ten percent Aura" with a further glance at her little sister she continued "And I shouldn't need to point out, weapons, Dust and Semblance are allowed. Expected, even"

"For the prize, winner kisses loser" Yang suggested

"That doesn't even make sense" Weiss protested

"If we must" Winter strode impatiently into the arena.

Weiss reluctantly followed.

As they stood facing each other for the countdown Winter looked at Weiss's relaxed pose and spoke again "If you respect me you will not hold back. I will expect you to bring your all"

As the buzzer sounded glyphs sprang into life around both sisters
Winter Summoned two alpha beowolves to her side

Weiss's more diffused effort resolved into six identical copies of herself, distinguished from the original only by hue. With a brief moment of eye contact, she stepped back and was lost in the crowd. As Winter struggled to comprehend what she was seeing, more glyphs sprang up forming a wall enclosing the combatants. Recognising the similarity to some of Weiss's previous moves Winter drew her weapon and braced herself for the onslaught.

The bombardment picked up quickly as the horde took moved back and began to bounce between glyphs. As her beowolves disintegrated under the first few strikes Winter managed to destroy one of the clones with her sabre, but even as she did so she was struck by three others. They where simply coming in too quickly, from too many directions. And, she belatedly realised, they could pass right though each other. She crouched down and tried to push her way to where the summoning glyph must be, unwilling to accept what was happening. A succession of shielding glyphs shattered under the relentless assault and she fell to her knees.

Winter opened her eyes to see Weiss and Yang kneeling beside her. She pushed herself to a sitting position, and glanced at the status board - it was blank. Seeing Yang pick up her scroll, she managed to catch a glimpse of a timer still running, thirty seconds. Subtracting the time it took for the attack to start and the time she was unconscious it was a very humbling figure.

Weiss looked at her sister with concern "Are you hurt?"

"I am uninjured" Winter managed to stand with only slight effort.

"I call that one Weiss-storm" Ruby remarked conversationally

Weiss shrugged awkwardly."I can only keep it up for a couple of minutes"

"It was most impressive. Effective," Winter grimaced, "if you opponent lacks the good sense to flee the target area"

"I was lucky"

"You knew my pride would prevent me from retreating until it was too late." She put her hand on her sister's shoulder "It was well fought"

Yang smiled "If it makes you feel any better, Qrow lost his lunch after Ruby introduced him to 'Twister'"

"I can not imagine why that would concern me" Winter remarked coldly, but her expression brightened. "I believe there was the matter of the prize"

"Winter-"

"It is a matter of honour" Winter insisted

Weiss rolled her eyes, but stepped towards the taller Schnee.

"No peck on the cheek cop-outs" Yang coached, holding up her scroll to take a picture

Winter was surprised how smoothly Weiss's hand guided her head as she captured her lips for a brief soft kiss, punctuated by the sound of Yang taking the picture.

"Welcome to the club!"

"I have absolutely no idea what you are talking about. That was hardly my first kiss"

Weiss scowled at Yang "An earlier, non-sensical conversation about kissing sisters, I'm afraid"

"Strange rituals notwithstanding, I am impressed with the progress you have made. It would appear that independence agrees with you"

Weiss smiled at her big sister. "It does. You should rest, I will escort you back to the barracks"

"I will not be nursemaided by my little sister"

"I'll go" Ruby quietly suggested.

Seeing only firm resolve in her sister's face Winter relented "That is acceptable"

Weiss hugged her big sister "Goodbye, Winter"

Winter stiffly reciprocated, clasping her arms around Weiss. "Until next time, sister"

Winter nodded to Blake and Yang "It was... interesting to spend more time with you"

Yang listened to their conversation as they left the arena.

Winter turned to Ruby "It seems I am presented with an excellent opportunity to get to know you."

"Ok, ask away"

Thanks to Winter's firm, clear, speech the first question was just audible to the remaining group.
"When did you first experience homosexual urges towards my sister, and what were the nature of those urges?"

Weiss and Yang shared a glance. The possibility that Ruby might answer honestly was too horrible to contemplate. Yang turned quickly to Blake, "I should go with them", giving her girlfriend a hasty peck on the cheek she ran off to rescue her little sister.

The projectile flew through the air, headed for Winter's face with pinpoint accuracy, only to be blocked by a glyph and reflected back the way it came. There was a startled yell from the rooftop as juvenile delinquent got a face full of decomposing produce.

"Nice one!" The sentry caught Winter's severe expression "... Ma'am" he saluted nervously.

"Indeed" Winter quietly agreed as she stared at Ruby.

"What. Was. That?" Yang's words slid out between clenched teeth, accompanied by a faint sizzling noise. A brown-red substance, possibly once a tomato was dripping though Yang's hair. Her eyes were red and she was beginning to smoke slightly.

"I'm sorry to say the local delinquents consider harassing military personnel to be a rite of passage"

"Rite of not being able to sit down for a week" Yang muttered darkly as she strode off in the direction of the warehouse their attackers had been using as a platform.

"So, those buildings aren't valuable or anything, are they?" Ruby asked conversationally.

"Not particularly" Winter turned abruptly to the guard post "Miss Rose will require a guess pass. She will be accompanying me to my quarters"

"I will?" Ruby paused as Winter grabbed her wrist "Uh yeah, I guess I will"

The guard tried very hard not to give the strange couple any sort of look at all as he handed over the pass.

Winter strode though the maze of passages inside the barracks dragging Ruby behind her. Reaching a doorway that looked like all the others, she opened the door and all but shoved Ruby inside. Stumbling into the tiny room Ruby tripped and fell onto the bed. She watched as Winter followed her in, closing the door and locking it.

"Now that we have some privacy, I believe we should get straight to business"

Sprawled on the bed, Ruby gave a nervous laugh "I'm kinda serious about Weiss, so it would have to be a Schnee-some"

Winter's expression went blank "Pardon?"

Ruby belatedly realised she had possibly made the worst joke in 'meet the family' history, a disaster that could only be mitigated if Winter didn't get it "Um, nothing. You wanted to talk?"

"A crude pun, alluding to a sexual three-way with Weiss and myself, yes?"

There was no way to spin that. Ruby sat up straight and blushed, looking down at her feet "Yes. Sorry"

"We have more important matters to discuss. My aura won't recover for hours yet, we both know I didn't generate that glyph at the gate"

"Oh, that"

"There has only been one other incident where someone outside the family-"

"I'm not pregnant"

"It seems you know a great deal about our semblance" Winter paced, though in the small room it was only a couple of steps back and forth "She had no control, anyway"

Ruby sighed. "The Schnee semblance can be copied, that is how the family thing works. Weiss and me are ... close, so it tends to rub off a bit. It doesn't last long"

"Why?"

"Why what?"

"Why did you do it. It was reckless. The trouble this could cause, the semblance is important. It-it's what it means to be a Schnee"

"You needed help. You were the only one who would know"

"I wasn't in danger"

"You would have been humiliated in front of the guard"

"That isn't important"

"It is important to you. Weiss would have helped you"

"Weiss is my sis-"

Ruby rose quickly from the bed and took Winter's hand. "Which makes you my sister." after taking a breath she continued "Knowing how Weiss feels... feeling what Weiss feels, it's part of how this works"

"Oh" Winter sat heavily on the bed. After a long pause, she released Ruby's hand and started speaking quietly "I don't mean to be this way"

"What way?"

"Cold. Angry. Arrogant"

"You're not-"

"I hear what people say. And I don't mind, not really" she swallowed. "With Weiss sometimes, I want- I try-," she shrugged "but it comes out wrong. Could you tell her that I-"

"You should tell her yourself, next time. But she knows, that you love her, that you care about what she does" Ruby smiled "And she loves you too"

"Thank you"

"I should find Yang before she does too much damage. Am I allowed out on my own?" Ruby opened the door.

"Yes. This isn't a secure area. Can you find the way?"

"I think so. If all else fails I'll set fire to something and get thrown out"

"Please don't" Winter's colleagues would have been surprised to see the faint smile on her lips as Ruby closed the door.

Author afterword: I don't like to over explain, but given my erratic out of order publication schedule I'll mention some stuff that I would have preferred to imply in the sequence of stories: Ruby and Weiss's personalities are changing (not [just] my bad character work), they are hiding something, and their abilities are advancing at a terrifying rate.