Theresa Apocalypse is a clone made from the DNA of Kallen Kaslana and a Honkai Beast named Vishnu. She is also the principal of St. Freya Academy and the World's Cutest Valkyrie (in her words). Due to experimental shortcomings, Theresa's body could not physically grow up past the age of 12.

As Theresa rose through the Valkyrie ranks, she soon lost her fellow Valkyrie and friend Cecilia, in another battle, watching her death on a live camera. Theresa wanted to flee with Siegfried and Kiana, Cecilia's husband and daughter respectively, by sneaking them out of Schicksal at night. Otto suspected Theresa might do something and dispatched his men to prevent Theresa from deserting. Having obtained Kiana, Theresa was forced to leave her behind to save Siegfried. Otto managed to have Theresa surrender after his men recaptured Kiana. Theresa had a list of demands that she wanted Otto to fulfill before she agreed to stay. These demands included the creation of a branch in the Far East with a school she would run to teach Valkyries.

While she does have a somewhat mature personality, she does display a fondness for child-like things (sweets, HOMU) and many of her battle phrases involve her calling herself cute or insulting the enemy. Sometimes she also uses her cute appearance to her advantage. Despite her occasional immaturity, she is a very capable principal of St. Freya High and will do anything to ensure her student's safety.

CN Voice Reference: https://www.youtube.com/watch?v=mUHLvDc8T1s