Eternal Calculus

Eternal Calculus is a 5★ weapon in Honkai: Star Rail.

Eternal Calculus was released on January 1, 2001. They were introduced alongside Before the Tutorial Mission Starts, Solitary Healing, But the Battle Isn't Over, Sleep Like the Dead, Hey, Over Here, On the Fall of an Aeon, Night on the Milky Way, In the Name of the World, Cruising in the Stellar Sea, Texture of Memories, Moment of Victory, Something Irreplaceable, Time Waits for No One, For Tomorrow's Journey, suggesting they were part of the same content update.