Shibata no Ono

Background
Shibata Katsuie was a military commander during the Sengoku period, serving Oda Nobunga as a retainer. Known as the "Oni Shibata", he was forced to execute his own brother, he broke a siege with an all-out attack, and attempted to conquer the Hokuriku region. It was during this siege upon the region that he met his demise. During the Battle of Shizugatake, he attempted to besiege Nakagawa Kiyohide to turn the tide of a losing battle. Ignoring his superior's orders, his force was destroyed by the forces of Toyotomi Hideyoshi. Retreating to his castle, he had to surrender after the loss of his army, and was forced to commit seppuku after setting fire to the castle.

Shibata's axe survived, of course, but after 50 years of enduring its master's failures, tragedies, and bloody battles, the axe had grown resentful, and eventually evil. It was one of the few things that survived the destruction of Kitanoshō castle.

Following the death of his master, the axe of the famed 'oni' ended up in the hands of another warrior, and in many more battles during the Sengoku period, where it continued to grow more evil as it was used more to kill, and many of it's wielders would grow to become great warriors during the course of the wars. As it changed hands many times during the period, it became more evil and resentful with the experiences of each who used it, and it grew to crave blood as it cut down many more.

The Sengoku period ended, and the Azuchi-Momoyama period began, but there were still many battles for the axe to participate in, as it grew more evil and caused more bloodshed. It fell into the possession of one of the retainers of Hideyoshi Toyotomi. After his death, it was finally lost somewhere in Japan.

Almost directly after Hideyoshi's death, came the Edo period, which signaled peace in Japan for a long time. The axe was never in any recorded events, but several reports of madmen on killing rampages with a cursed axe were reported during the period. When each one died, his killer would grab the axe. With each one the killing would begin anew as the axe began to corrupt it's wielders, but there seemed to be no end to the bloodlust of the axe.

The last person to wield Shibata no Ono was unsung hero who took hold of the axe, after a great battle with the previous wielder. This hero realized it's danger, and sought to finally destroy the axe for good, going on a great journey accross Japan. But Shibata no Ono managed to corrupt the hero, as it does all men. The hero would never be able to make it to his destination before the axe took control of his mind, so in a last ditch effort, the hero travelled deep into unknown lands where youkai roamed, coming upon Youkai Mountain, the hero sought a deep cave, which he sealed the entrance of, before Shibara forced the hero to kill himself in it's lust for blood. Reports of killing sprees ceased. It seems the axe had finally fallen into the unknown, never to be heard of in the world again...

Power/Combat
Ono is an axe that festers with power and evil. When it does not have an owner, it tempts those who come near it to pick it up with promises of power, or that it is valuable beyond compare.

When it is picked up, it immediately tries to give the owner feelings of ownership, and attempts to convince the holder that they should never dispose of the axe or give it away. If the mind is weak enough, it may even attempt to take control of the wielder's mind then and there.

Ono will bestow strength to whoever picks up the axe, and they will quickly find the axe is very light to them. It also feeds the wielder knowledge of how to properly use the axe in a fight, and will additionally increase the constitution of the user, although only gradually. For the longer it is owned, the more powerful the wielder will become.

If it is wielded for a long time, it will slowly attempt to corrupt the user's mind, feeding them increasingly violent and evil thoughts, corrupting them further, driving them to kill whenever possible, and eventually even taking control of the mind completely. It will always try to convince the user to carry the weapon around whenever possible, so it cannot be easily lost or stolen. If it has corrupted the mind enough, it will even force the user to wield it at all times.

With sufficient corruption, the axe's wielder will also begin noticing a young child, supposedly a projection of the axe itself, who will physically project the axe's thoughts, needs, and desires, and will often appear whenever the wielder thinks about getting rid of the axe, as the "projection" (possibly a delusion, even) will be sure to use whatever means it can to make sure the user continues to use the axe, whether it has to bully or plead or coerce. This projection will often harass the wielder as well, riding on him, or appearing suddenly to surprise him, among other pranks.

If Ono is first picked up during an intense battle or by someone in a desperate position, all of the above effects will be greatly intensified, perhaps driving the wielder into a berserk rage as well.

In a battle, Ono is a frightening weapon, intensified by the (increased) strength, skill, and toughness of the user. It can be invoked to cleave through the air and emit a powerful wave of energy in it's wake, which can slice with the same strength of the axe. Ono is a highly bloodthirsty weapon, and it will compel it's wielder to bathe it in the blood of others. The power Ono bestows is temporarily increased when it has recently been able to kill or maim others in combat, and will give the wielder a sense of euphoria when it has done this as well.

If Ono has gone for a long, long time without blood while it is owned, it will compel the user to kill themselves using the axe, if it is unable to fully corrupt the wielder. If it has, it will instead go on a berserk rampage with the user, killing anything it can until the user expires.

Ono is an evil artefact weapon of great power, and is supernaturally resistant to rust, corrosion, and wear. Any mundane attempt to damage or destroy it will be ineffective, and additionally will cause it to assault the mind of whoever struck it the moment it was touched. To truly destroy it would require an action by a major god or higher being, destruction by another artefact, or for it to be melted down on a sacred ground, such as in the bubbling magma of Mt Fuji.

Ono could perhaps one day become a Tsukumogami, but it enjoys the feeling of corrupting it's wielder too much, and the power of souls flowing through it's steel is better gotten through someone else's anger. Being able to move on it's own and wield itself might be quite a lot more dangerous then the threat it presents now, however.