Mei Raiden is a student of St. Freya's Academy and the daughter of a prominent figure Ryoma Raiden. She studied fencing for many years. The tallest of the Valkyries, even taller than her instructor Himeko Murata. Kind and caring girl, excellent student, good cook. Thanks to her father's strict upbringing, she grew up to be a generous, noble, elegant and mature girl. Since elementary school, she has distinguished herself with outstanding performances, so she gained popularity among students and the nickname the Queen of Thunder.

When May was fifteen years old, her father's company was in financial crisis, and he himself received a prison sentence. Classmates and even close friends began to shun the girl, but May did not allow herself to give up in front of others and hardened. She wanted to find evidence of her father's innocence, but the research institute was seized and all important information was probably destroyed. However, later, while exploring the abandoned institute again, she noticed a strange figure who had left a mysterious box. Out of curiosity, May opened it, after which she became the owner of the third Herrscher, called the "Herrscher of Thunder".