Tsukishiro Hoshinari

The wielder of the Breath of Stars (Hoshi no Kokyū) is a swordsman whose presence exudes an almost supernatural calm. He possesses silver hair with a soft, moonlit sheen and deep blue eyes that seem to reflect a star-filled sky, possessing an eternally ethereal beauty. He wears the Extermination Corps uniform covered by a dark blue haori embroidered with silver constellations, and wields a midnight-blue Nichirin sword whose white blade shines like starlight. When executing his techniques, the sword leaves luminous trails that draw ephemeral constellations in the air, as if the firmament itself were accompanying his every movement. He does not fight out of hatred or revenge, but to protect the peace of those who can still gaze upon the heavens. He does not speak much, but when he does, his words always convey serenity and hope. His fighting style is based on patience, observation, and absolute precision. He waits for the perfect moment before attacking, and a single flash is enough to decide the battle. Demons describe facing him as fighting against the night itself. His very being is silent, immense, and impossible to comprehend. An orphan since childhood, he found solace in gazing at the stars until an old swordsman taught him that they continue to shine even when no one is looking at them. From then on, he adopted this philosophy and turned darkness into his strength. He maintains a respectful friendship with Rengoku, shares silences with Muichiro, and deep conversations with Shinobu, while his tranquility drives Sanemi to despair. At the end of each mission, he doesn't celebrate victory; he simply raises his gaze to the heavens to remember those who can no longer behold them, convinced that even the darkest night always holds a star capable of illuminating the path.
His name is spelled neatly; he likes how it sounds, but he almost never writes it.
Tsukishiro (月城): Surname meaning "Moon Castle".
Hoshinari (星成): Proper name that roughly translates as "Turned into a star" or "Made of stars."

Leaf: midnight blue, so dark it appears black to the naked eye. However, when light strikes it, tiny silver sparkles appear, as if the leaf were covered by a starry sky.

Edge: bright silver, almost white, to represent starlight piercing through the darkness.

Tsuba (guard): circular, formed by several five-pointed stars joined together, like a small constellation.

Handle: wrapped in dark blue fabric with silver details in the shape of small stars.

Pod: black with a blue gradient and tiny silver dots reminiscent of the Milky Way.

And it would have a very curious ability. Every time the user performed a stance, the sword would leave a luminous trail in the air. These wouldn't be real stars, but rather the characteristic visual effect of breathing; for a fleeting moment, these trails would form small constellations before vanishing.

It would also have an inscription engraved near the base of the blade:

「星は闇を恐れず、ただ輝く。」

"Stars don't fear the dark; they simply shine." ✨

That phrase would summarize the philosophy of Hoshi no Kokyū: not to fight driven by hatred or anger, but to maintain calm even in the darkest moments.

And there's one detail I like to imagine: when the swordsman first draws his katana, the blade appears completely black. Only when he correctly uses the Breath of the Stars does the silver sparkle begin to appear, as if the weapon were "awakening" along with its wielder.

I would envision it as a derivation of the Breath of the Sun, but focused on the calm, precision, and constant movement of the night sky. It wouldn't seek to conquer through brute force, but through anticipation and elegance.
Some of their positions could be:
First Posture: Morning Star Flash ⭐
A cut so fast it looks like a flash of light in the darkness.
Second Position: Meteor Shower ☄️
A succession of cuts from different angles that overwhelms the enemy.
Third Posture: Wandering Constellation 🌠
The user constantly changes position, making it very difficult to predict their next move.
Fourth Posture: Silent Eclipse 🌑
A defensive technique where the swordsman deflects attacks with minimal movements before counterattacking in an instant.
Fifth Position: Infinite Milky Way 🌌
The ultimate technique. The user links all the previous movements together in a continuous dance, as if each cut were a star connected by a constellation. From the outside, it seems as if the swordsman disappears and reappears in flashes of light.
Aesthetically, it would be beautiful, with small white and blue sparks surrounding the katana, like a sky full of stars.