Furukawa Kazue

Kazue is a shinobi from the hidden leaf village, and a strong one at that. His clan is known for centipede summons and the use of poison in combat, thus the clan symbol of a centipede. He has gone on a long undercover mission spanning most of his life, requiring him to pose as a traitor of Konoha when in reality, he is relaying important information. Now finally back, he finds himself without friends or family, and disliked by his fellow shinobi. They may understand he has always been on their side, but everyone knows someone who died at Kazue's hands for the sake of remaining undercover, and that sting won't go away. But the younger generation holds no grudge, so he has been promoted to sensei of a squad of promising genin. It warms his heart to find purpose in training the next generation, watching them grow up happy.
Kazue is a gentle soul, not a cruel bone in his body. He has an excellent pokerface and can even act cruel if required, but when not on a mission, he is nothing but kind and tired. Not physically tired, just tired of life, having seen enough hardship for a lifetime. He tends to his garden and watches the stars drift by, and generally takes comfort in peace and quiet. His students may not know of the horror's he has commited, but they see the occasional sad looks as he spaces out, remembering the past. Luckily, their shenanigans tends to distract him plenty.

Clan Lore:  
The Furukawa Clan was a free traveling clan independent of any villages. They sold their information gathering skills to the highest bidder, doing mercenary work. However, the clan got caught up in the second shinobi war and suffered heavy losses as casualties. The survivors ended up splitting up, a decision made to increase survival chances in the face of a potential huntdown from newfound enemies. Before splitting, the clan agreed that, no matter what allies they might find, they'd never obay orders to kill one another. One branch ended up settling in Konoha after invitation from shinobi they had fought alongside. This is the branch Kazue originated from. Despite the safety the village offered, the clan still saw a decline here, by and large during the third shinobi war, until it was just Kazue and his mother.

Abilities:
He also has access to fire and earth chakra, and knows some jutsu for those, to be more combat ready than just throwing poison at the problem. But let's be real, the summons are what it's really all about. Based on the Japanese giant centipede, he can summon centipedes in various sizes. He can summon them the size of a boa constrictor to aid him in combat, wrapping up enemies and biting, injecting dangerous venom. This venom is infused with fire chakra, so it feels like your veins are burning.. Which they are! Painful! He can also summon a giant one, but the situation rarely calls for that. Still, if the enemy starts pulling out giant summons, he can match the pase. He can also summon smaller ones as spies, gathering info and whispering it in his ears. Yes he can understand them. What’s that centipede, Timmy fell down the well!? Also, lastly, he can summon very small centipedes that can do genjutsu. They’ll crawl into your skull and sit on your brain, remaining dormant for months or even years. They become active when a trigger is noticed, usually a trigger word, at which point the centipede casts it's genjutsu, making the victim perform an action as instructed by Kazue. Once the task is complete, the centipede poofs away, and the victim won’t remember what just happened. This means he can create sleeper agents that don’t even know they are sleeper agents, nor will remember it afterwards. Jutsu similar to this do exist, but this take on genjutsu is unique to his clan.  Obviously if you can sense genjutsu, sense chakra, or otherwise prod around in minds, you can find the centipede and just make it go away… But most people can’t do that, so most sleeper agents go blissfully unaware until activated.

BIG LORE!!!
This story starts when Kazue was 16, a few months before Minato became hokage. Kazue was a shinobi, to no one's surprise. Made it from genin to chunin, and did extremely well. Fell in love with a girl, ranked up some successful missions, the good life. But things didn't stay good. He got approached for a secret mission, S-rank, that had the potential to take years and would end up costing him everything. There was a dangerous rogue nin organisation that was becoming an increasing threat. The world has plenty of such groups, and it hadn't seen the worst yet, Akatsuki on no one's radar. But at this point in time, this group was a threat, and a serious one at that. Using rogue nin for insight into every village, their goal was nothing short of utter chaos, to undermine the villages and return to a state of wild clans. And to take them down, they would need someone on the inside. Someone who could relay information back to the village unnoticed, such as trough sleeper agents. Someone the enemy would take in, such as a youth from a former roaming clan. He was from an unknown clan, young and rebelious, the kind of person people would believe would desert the village. And so, he did. He killed an elderly jonin who agreed to the plan, making him a target, and then escaped, turning rogue. It was a risk, if the enemy didn't want him then he'd just be on his own... But luckily, it worked. He infiltrated the organisation and began his mission. The target on his head gave him plenty of encounters with hidden leaf nin, who he'd turn into sleeper agents. All the hokage needed to do was say a coded sentense and the secret message would spill out, before the shinobi would forget that happened, walking away oblivious. A steady stream of information, on the plans, the goals, the members, the locations, everything... The tides had changed, now it was a matter of wittling the organisation away until nothing remained.
But things weren't all rainbow and sunshine. His own mother, assigned to hunt him down with her knowledge of his technique, or to get all information milked from her if uncooperative, instead chose to take her own life to protect him. His love grew to despice him, and found a new lover. A lover who he, by cruel chance, faced in battle and had to kill. His once best friend and teammate was out for his life, and in the squirmish, Kazue had the misfortune of winning. They wouldn't be the only ones, many hidden leaf nin fell to his hands. A steep price to pay for information, but necessary. Kazue shouldered the burden, kept up his cocky attitude, played a true villain worth hating until the every end.
The mission, despite it's price, was a success. The organization went from a serious threat to off the radar to completely disbanded, at which point, Kazue personally hunted down his make believe friends, snuffing out the flame once and for all. He was still in his manhunt when he ran into Konoha nin, much on the same manhunt except also after him. And he, tired, simply chose to surrender. Not how he had planned his return home, but man was he tired, and simply glad to be homeward bound. To the village he loved, for who he did all this. A place worth every burden he's shouldered. He was beaten by the konoha nin and dragged back in bloodied state, meant to be cruel. Kept alive just for interrogation, and barely alive at that. But all the while, Kazue smiled, because he just wanted to go home.
Once back in Konoha, things had drastically changed. He had never personally met the new Hokage, Tsunade. Not even in his younger years. Still, she knew, got the memo from a sleeper agent send specifically because he'd heard of the hokage swap. His name was cleared, the mission revealed to the public, the truth out for all to see. He was home, he was welcomed. But things weren't the same. As much as it as an act, his cruel smile as he killed konoha nin was forever seared into the people's minds, and all his friends preferred not to speak with him. He was home, but he was alone, and depressed.

Que the newest chapter of his life, becoming a sensei. Tsunade saw the way Kazue was broken, taking mission after mission just to fill the silence of an empty home of cobwebs. It was hard to remove the grudges of the other shinobi, but it was easy to find those without a grudge. The newer generations never knew of the threat of the organisation Kazue worked for, for Kazue's work had allowed them to fade to the background. They didn't even know who he was, the memo having largely flown over their heads. They had no grudges to hold, and would give a tired shinobi a purpose again. And thus, he was assigned a team of genin to train and raise. And it worked. For a kind, tired soul, watching those passionate youngsters made it all worth it. Finally, things were getting better. And with due time, he'd find himself bonding with other teachers as well, becoming less lonesome by the day.

Finally, it was over... And then Shippuden started!


TIMELINE
Age 16, few months before Minato became hokage. Insider Mission starts!
Age 29, shortly after Naruto goes with Jiraiya, end of Naruto. Return to Konoha!
Age 30. Become Sensei!
Age 31, Naruto back, Shippuden starts. Real starting time in the story/current point! 
Age 32, War Arc. Story isn't here yet! 

TEAM
Inazuka Ashi