Bakuseiken

"The Zanseiken is a blade that pairs with Bakuseiken wielded by Kirinmaru. In ancient times, Amatsumikaboshi, the god of stars, gifted two swords. I have heard that the Bakuseiken and the Zanseiken were those two swords."

- Rion

is a cosmic demon sword wielded by Kirinmaru. It is one of the two swords gifted by the god of stars, Amatsumikaboshi. The other being Towa's Zanseiken.

History
According Kirinmaru's daughter Rion, in ancient times, Amatsumikaboshi, the god of stars, gifted two swords: Zanseiken and Bakuseiken in outer space, until, it impact on Earth.

Kirinmaru used it to fight with Tōga, the Lord of the Western Lands 600 years ago in the, and not too long, the samurai tried to kill him by the orders of , but they were no match for him as he broke the katana with his sword with ease, until his daughter is captured by a vengeful half-demon named Sakasa who tried to avenge his master's death, so he beheaded him but was shocked to see his body kill his own daughter and slashes his head turn as a skull.

Eighty-six years later, he used it to use Blasting Barrage to destroy the Grim Comet's layers while Tōga destroy the demons inside with the Meidō Zangetsuha. In the present day, Kirinmaru drew his sword to battle the half-demon princesses and then Sesshōmaru.

At the ruin of Izayoi's mansion, when Sesshōmaru went to attack Zero, Kirinmaru blocked Sesshōmaru's attack with his sword to protect his sister. After Zero and Sesshōmaru departed, Kirinmaru sheathed his sword and used the sword Riku had stabbed him with to fight the half-demon princess. After the blade was destroyed, Kirinmaru unsheathed his sword and used it to battle them, cutting through the blade of Setsuna's Kanemitsu no Tomoe and killing her, since Setsuna penetrate his barrier by her Blood Blade. He then battled Moroha and Towa, who gained more power due to their rage and grief, but he still managed to beat them.

After confronting Towa, Riku, and Rion; Kirinmaru saw Towa had the Zanseiken and drew his sword, ready to fight Towa with all his might. When he noticed, Towa could see Akuru, he re-sheathed his sword, so he could give chase. After keeping his sword sheathed while battling Moroha, Kirinmaru drew it to battle Sesshōmaru, and was overwhelmed when the half-demon princesses combined their attacks, and severely injured him.

Furious, Kirinmaru raised his sword and conjured up the Demon Fireball to attack them. Sesshōmaru stood in front an took the full force of the blast. After Sesshōmaru fell unconscious, and the princess got sucked into the Black Pearl, Kirinmaru searched for the Black Pearl, eventually finding it with Takechiyo, but he didn't draw his sword until Rin stood up to him. He didn't get a chance to use it though as Sesshōmaru reemerged, and Tōga's spirit knocked him away after the Tenseiga manifested it.

When Kirinmaru returned, he found Moroha and her parents Inuyasha and Kagome Higurashi standing against him. He used his sword to block all of their attacks, except for a sacred arrow fired off from a bow Inuyasha and Kagome had given to Moroha. He chose to dodge it instead, and clashed swords with the Tessaiga. However, he sensed Rion dying and retreated.

Kirinmaru used his sword to restore Rion's life force, and then battled her and Riku. Kirinmaru didn't draw his sword until near the end of the battle, and used it to block Riku and Rion's attacks. Kirinamru disarmed Riku, but found Rion holding the deceased Zero's staff at his neck. She hesitated, and he used the staff to stab Riku, and then fled with Rion.

Physical Description
It has a dark wine-red hilt studded with yellow, as does its sheath.

Abilities

 * Supreme Demonic & Stellar Energy Storing: Originating from the infinite cosmos itself, it possess nearly infinite amount of stellar power as well as that of demonic energy, being created by the almighty God of the Stars himself. However, such abilities are negative and quite destructive as they are lethal. These powers are equal to its positive counterpart.
 * Blasting Barrage: Kirinmaru slashes his sword and releases a large slash of energy that fires multiple powerful energy projectiles capable of destroying the Grim Comet and easily overpowering Moroha's temporarily enhanced Crimson Backlash Wave even when using Riku's sword.
 * Unnamed Wind Blast: Kirinmaru blasted Moroha with this strong wind, similar to Tsubaki's wind blast from her right eye, Ryūra's Wind Blast from Fūjinga, and Setsuna's Cyclone Burst attack.
 * Unnamed Black Hole Technique: Kirinmaru fires from his sword a powerful black hole that was strong enough to plow through Towa's gigantic demonic dog projection of her father and overwhelm her ability to absorb demonic energy to where she was knocked unconscious.
 * Demon Fireball: Kirinmaru had utilized this potentially fatal attack on Tōga in one of the many battles, which he eventually used to destroy the Half-Demon Princesses once and for all. Once it makes contact with a demon of any power level or status, the demonic energies it is comprised of is such that it gradually strips its target of their vital haku (demon and human's life-force essence allows the body to be mobile) until they perish entirely.
 * Life-Force Replenishment: Since his daughter Rion can't move her body, he use the haku from the blade to replenish her, so she could move again, aware that his daughter would soon be able to have enough haku energy to sustain her artificial body on her own.

Trivia

 * The way it has a powerful weapon of equal magical strength and abilities is just like the Moonstone from Rapunzel's Tangled Adventure, and the Scepter of Night from Elena of Avalor; all three can have their negative and fatal effects undone and neutralized by its opposing weapon possessing all existing positive forces.