Author Note:
Guys... about the ages of the characters, Mei is nine. The age of Konan, Rei, and Tsunade doesn't matter as they won't really age. Just think of them as 20 or something. As for Ringo, she should have been 16 right now. But really, don't take ages too seriously as even I started to have a problem keeping up with all ages of characters through these time skips.
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Mei sprang up on her feet and quickly jumped to the side to avoid a stomp from Rei.
"Good! You are getting quicker." She could hear but her mind had no time to react as yet another punch flew at her and she had to quickly decide where to dodge next. It was then she spotted Tsunade hiding behind a tree so she nimbly jumped towards it, evading Rei's punch. Rei didn't dally and followed her. He obviously knew Tsunade was hiding there but this was training so he played along with Mei's strategy and gave chase. The second he was close to the tree, Tsunade punched it which broke it in half and sent the upper half flying as Rei jumped above it to avoid it. Mei was already prepared for that and Rei was met with a lava bullet to the face... only to melt into water.
"Water Clone!" Mei exclaimed and instantly ducked. Not out of instinct but due to her being used to Rei mostly getting above the belt strikes when she is distracted. Rei was actually quite surprised the girl noticed this little flaw of his fighting style but he just continued doing so as it made it easier for Mei. Right now, he needed to give her some foundation and made her start using her senses and instincts during the battle. If she started to notice flaws in his way of fighting then clearly, he was doing something well.
He also had to jump back as Tsunade went for a save by trying to engage Rei in a fight. He stood opposite Mei and Tsunade who were watching him intently, looking for any opening. Mei was learning teamwork right now so she and Tsunade were trying to fight against Rei. The catch was in the fact they were forbidden to verbally communicate and Tsunade reacted only when it was necessary. Mei was forced to do all the work. Mei was forced to read Tsunade's body language to know what she would do next. Mei was also forced to create openings for Tsunade as she only joined the fight when the opportunity for a good strike arose. But most of all, Mei was forced to 'survive' while Rei attacked. He may have lowered his strength and speed so she could match him but as the fight went on, he was steadily increasing it.
As she ducked, she put her hands on the ground, springing her body into a handstand and her feet kicked towards Rei who blocked her kick with his right forearm and then twisted his arm to grab her ankle in one fluid motion. Rei often told Mei that this should never happen and even Tsunade didn't try to save Mei as she got caught due to her stupidity. Rei raised his hand and lifted the girl he was holding by her ankle until her eyes met his. He was momentarily amused by her scowl as she dangled upside down in the air but it was time to admonish her. "Mei-chan..." He eye-smiled. "What did we say about providing the enemy an opening like that? Clearly, you were supposed to either use ninjutsu or kunai there! Not trying to be cool by doing a handstand kick." He told her while shaking his hand up and down and with it, Mei.
"But..." Mei tried to protest but Rei stopped her by whipping his hand to the side, throwing her away. She did a few rolls in the air until she twisted her body in such a way that she landed on her feet into a crouch.
"Again." Rei sternly said and their training continued.
...
Rei sat down next to Konan on the blanket she prepared and started munching on a sandwich. "Hmm, these are good." He offhandedly told Konan who hummed in acknowledgment, her eyes watching Tsunade spar with Mei after their teamwork training was done.
"One more year and Mei will be ten." Konan said and Rei sighed. Ten years of age meant graduation. Graduation meant killing a classmate. "Are you sure you don't want to tell the Mizukage to get her through it via clan member graduation?" Konan asked.
Clan member graduation didn't require one to kill a classmate as clan children usually didn't even join the academy and instead were home-schooled until they were assigned to a team. This proved to be the right choice however as the clan kids were more prepared for shinobi life than the kids from the academy even after their first kill.
"I know Mei already had her first kill but I want her to kill someone by her own choice, not by a stupid coincidence of having her bloodline acting up." Rei said. It might be cruel that a ten years old kid would die due to his decision but this was bloody mist. Things like this were quite common here and Rei's priority was Mei. If it meant he would have to be cruel, then so be it.
"Okay." Konan said and kissed Rei. "Don't worry. I made sure she would be mentally prepared for it." She stated. It was then they saw Mei about to score a hit onto a Tsunade, only for a bone to stick out of Tsunade's forearm, blocking Mei's fist. "Who would have thought Tsunade would be able to replicate Kaguya's Kekkei Genkai." Konan dryly said.
Tsunade was working with their Kaguya 'guest' for more than a year and every time she experimented, her expression was getting brighter and brighter until one day she proudly and smugly showed Rei and Konan her new Bloodline. Apparently, she found out how Kaguya's body works and why they could do what they could do, and the rest was easy for her. With a bit of medical treatment, Tsunade made herself able to utilize the Shikotsumyaku. She said it wasn't even that hard.
"Must be nice..." Konan whined. "To be smart." If there was one thing she was jealous of when it came to Tsunade, it was this. Despite not looking like it, Rei knew that Konan wanted to get stronger because she knew only strong people won't be trampled upon. And when Tsunade's strength rose by a magnitude just by getting the Kaguya bloodline... Even Konan got a bit mad.
Rei just quietly patted her head in order to calm her down. "You have your own strengths."
Konan smiled at that but then her expression darkened. "What about Ringo?" She asked. They had a fight because of what she did but it didn't really last that long. Both she and Rei couldn't stand being angry at each other so their 'fight' didn't last even half a day. But since then, they haven't seen Ringo at all. For the entire year at that. Rei was quite exasperated because of that but he was slowly accepting it. Konan however didn't regret anything because she knew what she said had an effect on the girl. But even then she had no idea it would take so long for Ringo to come to terms with it! It was an entire year already!
"Last I asked she is being run ragged by the assassination missions. She has at least two per month." Rei said with a sigh.
"Yeah... we should probably start preparing for the war too." Konan said, knowing full well that Rei had non-stop ten clones making seals for their use. They knew it was coming and they were doing their damnedest to prepare. She frowned. "Mei will be genin for one to two years before the war starts."
"I guess we'll just have to trust she will be ready." Rei said shruggingly, making Konan snort.
"She is already on the level of chunin and that's without talking about her bloodlines you so painstakingly nurture." Konan rolled her eyes. "I am more afraid of her mental side rather than her skills. She is too youn-"
"But so were we." Rei interrupted her and looked her in the eyes which calmed her down.
"I suppose that's right." Konan nodded. "Well... I think we will just have to adjust her mentality..." Konan let out a long whine. "That means shitty missions." She let herself fall on her back.
Rei just smiled and leaned onto her, giving her a quick kiss. "That means shitty missions." He quipped amusedly.