Astharoshe "Asthe" Aslan, Duchess of Odessa and Kiev, is an undercover agent for the New Human Empire. She is a direct, no-nonsense individual who has a very low opinion of Terrans, referring to them as barbaric and stupid, among other things. Her opinion of humans, however, seems to have primarily been formed through Empire propaganda combined with having little exposure to or understanding of humans. Asthe takes being called a "vampire" as an insulting slur, and only refers to herself as a Methuselah. Asthe fights with a weapon called the Sword of Gae Bolg. The most powerful close-combat weapon found amongst the Lost Technology relics, the sword uses ionized xenon gas to create a high-density, high-temperature plasma blade capable of cutting through anything.

Asthe's view of humans begins to change after she is sent to Venice to arrest Endre Kourza, a vampire mass murderer whose newest round of killings in Vatican territory could spur a war. As part of her mission, she is partnered with Father Abel Nightroad from the AX Agency. When the two find Endre, Asthe becomes solely focused on killing him because he murdered her partner. She is so blinded by her rage that she destroys the Rialto Bridge, killing and wounding many humans that had come for a festival. Abel also sustains injuries while protecting her from her own sword, which flew back at her in the explosion. She greatly regrets her actions, and keeps a better handle on her emotions when they go after Endre again and arrest him. Though she initially berated Abel for calling himself her partner, a word of special meaning to Asthe, at the end of the mission, he earned her respect enough for her to call him her partner. She also became more accepting and tolerating of humans in general.

Her partnership with Abel would become an important step in the secret peace negotiations between the Vatican and the Empire. She would later be assigned to shelter the Vatican diplomats and the Earl of Memphis after the Rosenkreuz Orden's attempt to assassinate Cardinal Caterina. Through this turn of events, Asthe would also become a core Empire representative in the question to stop the Rosenkreuz Orden's continued efforts to start another war between the Methuselah and Terrans.

In the novels, the partner that Endre killed was the Countess Len Yearnoshe, however in the anime series, her partner is changed to a male and it is implied that they were lovers.

In the anime, she is first sent to investigate an incident suspected to be connected to a vampire mass murderer and reluctantly partnered with Abel, Astharoshe is a direct, no-nonsense individual who harbors a low opinion of humans. Despite the fact that she can be harsh, Astharoshe has also been shown to be very caring and understanding on some occasions. She has proved to be a skilled fighter and wields a large spear, that can extend on her command and fires massive blasts of energy from its tip.