The Tenth Pillar. (Kimetsu No Yaiba X OC)

Final Moon

The time froze.

All the Hashiras felt like their blood stopped running through their veins. Gleaming eyes and wide mouths were plastered on their faces.

Just before their eyes, the tenth pillar just had a metamorphosis.

His raven colored hair had rapidly grown waist-length. A bluish-gray, bandage-like carapace wrapped around his torso descending through his right arm, up his neck, and over the nose and mouth forming a mask. Black, flame-like tattoos spread across his chest and wrap around his left arm, and the remains of a tattered black cloak cover his lower body.

"Tensa Zangetsu, second night: Final Moon." The boy spoke. "While I'm in this form, I can perform the final Getsuga Tenshou."

Muzan could only watch the spectacle in front of him.

He was a demon lord, the king of the night, the one who has beaten death itself. But now, he's a witness. Right in front of him, the moon itself was baring his fangs again him.

Smokey black Reiatsu slowly danced around the shinigami, it was mostly focused around his right arm.

"The final Getsuga Tenshou, it's me becoming Getsuga itself." Hiiro spoke with his usual calm tone.

His golden eyes were totally focused on the demon.

The battlefield was under a sepulchral silence. Not the demons slayers nor Muzan moved an inch.

All the eyes were on him.

Shinobu felt her heart racing, deep inside she had a hunch. The amethyst eyed girl knew that this ability was a trump card, no, more than that it was like a desperate measure.

Her sixth sense was telling her that the boy doubted whether revealing it or not, like there's a huge price to pay.

Her mouth opened, but words did not came. They were stuck inside her, she wanted to stop him, that nad feeling was telling her that she should stop all this, but, other side of her wanted to end it all and that skill of him could be the last push they need.

She bit her trembling lips.

"Sensei!" An injured Inosuke stood up, covered in bruises and cuts, with his boar mask shattered and his dual blades at the verge of breaking. Even when he was in that state he cheered his master. "Kill that demon bastard!"

"Sensei, please end this!" The young Kamado begged as he summoned every ounce of strength to stand up.

Kanao Tsuyuri lend him her shoulder so he can stand again.

"Sensei! Kill him! If this end I can marry Nezuko-chan!" The lightning breathing user cried.

Soon, the others joined to the three idiots. Most of them were barely standing, severely injured and just two steps away from the gates of the lady of the underworld.

"Kojima-san, please avenge Sabito!"

"I'm praying for your success, Kojima-san."

"Onii-chan! Kill him, avenge Kanae-nee!"

"Kill him, Kojima-san. For Mitsuri and for me!"

"Hiiro, you bastard! Kill him! For Kyojuro and for Kanae!"

"Hiiro-kun, end this!"

The insect pillar smiled.

This was the smile she regained when she met him, when she accepted her feelings, when she kissed him the first time, the smile she had when the memories from five years ago came back, the smile she had when he came back to fight against Douma and Kokushibo, the smile she had when his body gave up and fell to her arms after Upper Moon one was defeated.