Yang

Duality.

All things are dual: good and bad; hot and cold; day and night; male and female; hard and soft; Yin and Yang.

Sen believed in duality. But often the balance tips, leading to disaster.

Sen didn't just believe duality, he knows duality. As soon as he discovered his semblance, he saw duality itself.

The other Sen inside him, equal but opposite.

His carer (that's what Sen calls him as it's the best description) told him that to master his semblance and aura usage he must learn to see his other side.

Sen never knew what that meant, and now was not the time to think.

A King Taijitu emerged out of the trees, the two snake heads hissing at Sen.

The King Taijitu is also an example of duality, wwith their black and white heads working together as a perfect killing machine.

No time to think about that.

Sen opened the pockets in his legs and grabbed the Pan-Long (his weapon). The Pan-Long assembled itself into two tonfas, Sen held it as swords holding the shorter part of the stick, his fingers gripped between the handles. He yelled as he charged at the black head. The black head swirled sideways to dodge the attack while the white head opened its mouth to attack Sen.

Sen turned and swung his right tonfa towards the fangs of the snake. The white head retreated back as the black one started attacking again. Sen then turned the tonfas around to use them as hammers. He used the branch section of the weapon to block the black head's attempt to bite. Sen yelled again, pushing the weapon, snapping the black head's fangs. Sen did a back flip and then leaped into the air, raising the weapons above his head and hammered it down onto the black head. With a cracking sound of the skull the black head laid still.

The white head swooped in, knocking Sen flying towards a tree. Sen stumbled up.

"We're playing this game huh? Come on! Your little buddy's dead, now let's 1v1!"

Sen triggers the Pan-Long so that it transformed into a bo staff.

The white head charged at Sen, who held his staff, running towards the snake grimm.

The head opened its mouth to swallow Sen but he sidestepped away, thrusting the staff through the red pupil-less eyes. With a jerk, the head collapsed as the grimm disintegrated.

"You know that your weapon has a blade for a reason," said an old man approaching the now-exhausted Sen.

"Hi sir."