That morning, Tendo, Sakura, Sasuke, and Kakashi were all going to the bridge with Tazuna-san to protect him. He stopped working for a while because Kakashi was out but since Kakashi had recovered, he had re-started working on it for a few days. As they got to the bridge, they noticed a bunch of dead bodies lying there on the ground.
Tazuna: "What's this?!"
He ran to one of the builders who were barely alive and held him up just a bit.
Tazuna: "What?! What the hell happened?!"
Builder: "A-a-a monster...."
Kakashi: 'Can it be...'
Tendo: "It is. Byakugan!"
As his Byakugan activated, multiple cracks appeared on the ground as a wave of his chakra flew out from all of his tenketsu, making the air extremely cold.
Sakura: "W-why did the a-air suddenly get so c-cold?"
Kakashi: 'His chakra feels like its getting more and more powerful by the moment! I see the number one rookie title of this generation isn't undeserved one bit. But his attitude...sigh, not now. I have more problems to deal with.'
He didn't intend for just the activation of his byakugan to be so powerful, but he had noticed over the past few days that his Byakugan had been getting more and more powerful every time he had activated it. He could already see up to 5km and his vision was starting to allow him to see opponents movements in slow motion, almost stepping into the territory of the Sharingan.
Tendo: 'This must be some sort of mutation of the Byakugan because of my Senju bloodline. Lately, I feel like something is gonna awaken inside of me but I can't say what it is. All I know is that the size of my chakra pool and its destructive power has been rising rapidly. But now is not the time for that. I already see them approaching.'
Mist started to form and a familiar voice rang out in the atmosphere.
Zabuza: "Long time no see, Kakashi. And I see you've brought back that sneaky ice brat with you. The rest of those brats are shaking but this one keeps looking at me with that smug look on his face. Hmph, Haku, make sure to wipe it off of him nicely."
Haku: "I will."
Zabuza: "Be careful, Haku. That one is certainly impressive but he's even more crafty. He clearly doesn't have the power to beat you so he'll try to catch you off guard and outsmart you. When he does that, it might be game over because that Ice Jutsu he used is lethal. Don't make the same mistake I did by underestimating him."
Haku: "...I understand. Although he's only a genin, managing to outsmart an opponent of your caliber is certainly impressive. But, I have a bone to pick with him, so he will not survive past today."
Zabuza: "Good. Haku! We have gained the first advantage, Go!"
Shwinnggg! Haku appeared behind Tendo and Sasuke while attacking with his senbon. Tendo blocked the hit with the chains on his hands then grabbed Haku's hands while throwing some senbon at Haku with the other. Haku was surprised at his skill with senbon but he easily ducked down, dodging the attack and delivering a sweep kick at the same time. As Tendo was still holding on to his hands, he couldn't use the full power of the kick but he used enough for a genin to not be able to block it, at least in his eyes they couldn't.
Tendo re-affirmed his thoughts about his eyes mutating when he saw the kick coming towards him in slow-motion.
Tendo: "Hidden Snake Hands!"
Three big white snakes slithered out of Tendo's sleeves and locked onto Haku's arms, wrapping it tightly. Tendo then jumped back, barely dodging haku's kick, and made a hand sign with one hand.
Tendo: "Water Style: Water Bullet Jutsu!"
A medium-sized bullet made of water came from Tendo's mouth and flew towards Haku with incredible speed. Haku was trying to free his hands from the snakes already so the size and speed of the water bullet coming towards so suddenly caught him off guard.
Haku: "Zabuza was right. He's much more than a genin so if I fight him as such, I'll only lose."
Tendo could feel his snakes fall onto the ground as if they had grabbed onto nothing. He knew Haku had disappeared from the spot and the Water Bullet landed down on the bridge, breaking a good part of it in the process.
Tazuna: "Hey! Watch the bridge!"
Tendo: "Be quiet and stay behind the girl."
Tendo was very serious about his missions because of who he was in his past life. He knew what he had to do to protect the client and he wouldn't allow any harm to come to the old man. Provided that he was still on the mission, of course. All grievances can be sorted with the client once the mission is over. That's what his old master taught him.
Haku appeared in front of Tendo unharmed and a log replaced his earlier position. Tendo noted how fast his opponent was at using the technique and kept it in his mind, using that information to formulate a new strategy.
Zabuza: 'I see, not only can he keep up with Haku's speed but his taijutsu skills which I thought were subpar the last time was actually a front. He wasn't even trying to hit me. Interesting...'
Kakashi: 'Hmm...'
Sasuke: "Hey! Stop trying to fight him by yourself. Let me help you."
Tendo: "...help me? Alright, fight him with me then."
Kakashi: "Hm? Is he actually willing to fight with sasuke? Sakura! Take Tazuna and back off. Protect him well! Let Tendo and Sasuke fight him."
Tendo knew Haku was a powerful opponent but he would never actually use a teammate that was weaker than himself in a life or death fight. That would only be a liability. The only thing he wanted to use Sasuke for is bait. He knew Sasuke was going to eventually get himself severely injured so he was planning to strike at the time when Haku least expected it.
Haku: "Are you from the Yuki Clan?"
Tendo: "..No."
Haku: "Then how are you able to use Ice Release?"
Tendo: "I was just born with it."
Haku: "Then, I don't wan-"
Tendo flickered in front of Haku as a blue aura appeared around his entire body. He threw a punch that left a blue streak in the air, zooming towards Haku with powerful force. Haku threw up his hand to block, but that's when Tendo's punch weaved past his hand, now picking up more force than ever. Haku barely dodged the attack but just the force from it had left a crack on his mask.
Haku: 'What a fluid taijutsu technique! It's like his hands didn't have any bones in them!'
Sasuke took the chance and appeared next to Haku, brandishing his kunai and then he attacked Haku causing the latter to barely dodge once again.
Tendo: 'His speed is certainly not lacking. But in time, all of this will be over. Water Style: Hidden Mist Jutsu.'