Eternal Calculus

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

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