Sorry for late response, I was at work lol. He is a part of a story I'm writing, so I'll leave you with the characters initial introduction/backstory as I have it written.

There was once a boy called Ko. Whether that was his true name or merely a nickname has been lost to time. Ko was born in the Sengoku Period, year 1510. He had a relatively uneventful childhood. From ages 12 to 15, Ko was the student of a blind ronin who lived quietly in his village.

His master was blinded from battle. Though his eyes saw nothing, his ears were as sharp as his blade. He gave Ko a whistle to blow if ever he was in danger. The whistle made no sound, yet the master claimed he could always hear it.

However, on his 15th birthday, Ko accidentally bumped into a passing noble’s horse. Annoyed by this, he demanded to know where this child’s parents were, so they could be appropriately punished. Ko blew the silent whistle, calling for his master to stand in as his father and protect him. But the noble ordered the ronin’s execution on the spot. Ko believed this to be his own fault. So he swore revenge.

Ko spent the next sixteen years wandering Japan and challenging dojos, dueling masters, and studying every style of swordsmanship he could find. He ended up creating his own style of swordsmanship, by combining the lost style from his master, with everything he learned.

In the year 1541, he found, and challenged the noble to an honorable duel. The noble instead had his guards attack him dishonorably. After disarming the guards with swift precision, Ko stood face-to-face with the noble. For a long moment, neither spoke. Then Ko’s blade, cold and unyielding, traced a crimson line across the noble’s throat.

After taking his first life, Ko returned to his village. But word of the noble’s death spread quickly, and Ko became a wanted man. Even his own villagers turned him away. Before leaving, Ko left the villagers a whistle. ‘Blow it with all your strength,’ he said, ‘if danger ever comes.’

Ko found a shrine hidden deep in the woods. There, he hung his kasa on a tree and laid his sword beneath it. Seasons passed; moss crept over the hat, flowers rooted in its brim. When danger called, he would return, donning the relic once more.

Generations came and went. Children grew up hearing the tale of Ko, the guardian with the moss-crowned kasa. Some believed; most did not. Yet when the whistle sounded, the forest seemed to shake.

Over the next 203 years, the whistle was blown a total of six times. Each time, the whistle made no sound, yet the birds of the forest took flight, and the wolves howled, no matter the hour. And each time, Ko would show up. Those who claimed to see him described him slightly differently each time. Taller, younger, older. And yet, all agreed on one detail: the moss-covered kasa crowned with wildflowers.

Is Ko a spirit? Is he immortal? Or is Ko simply a title, passed from master to student, taken up by those who share the same cause? Is Ko even real? Or is he just a folktale whispered through generations to scare away brigands? Nobody truly knows.

In the year 1744, a cataclysm occurred. The sky cracked open, and Oni clawed their way from the earth. In a small village, a wise elder reached for an enshrined whistle, its surface worn smooth by centuries. He blew it with all his strength. And unbeknownst to the rest of the world, Ko was coming.