Hayato Kisaragi is the main protagonist of Hundred. He is the older brother of Karen Kisaragi originating from Yamato prior to the Second Attack, but later moved to Gudenburg due to their father's job where he befriended Emilia Hermit until his parents' death, then moved to an insitutute in Yamato. 

Hayato was later scouted to enroll in Little Garden with both his tuition waived and under a scholarship under the condition his little sister would receive the treatment she needed due to his high aptitude for a Hundred, as a result of him being a variant and become a first-year student in Bugeika High School. 


The story begins with the Hundred, the only weapon that can counter the mysterious Savage life form attacking Earth. To become a Slayer (master of military arts) who wields this Hundred, the main character Hayato Kisaragi successfully enrolls in the marine academy city ship Little Garden. However … 
 
"I wanted to meet you, Hayato!!" 
"W–who are you…?" 
 
Hayato feels a strange yet familiar sense of incongruity towards Emil Crossford, his roommate who somehow knows him from somewhere. On top of that, as soon as he enters the school, he is challenged to a duel by the "Queen" (the school's most powerful Slayer) Claire Harvey! 
 
(Source: Anime News Network)

"Hundred"—that is the only weapon that can oppose the mysterious life form "Savage" from visiting the earth.
The protagonist, Kirasagi Hayato, aims to become a Martial Arts Master using this Hundred. He managed to get into the battleship university Little Garden.
However—
"I wanted to see you, Hayato!!!"
"H-How do you know my name?"
Around the roommate, Emil Crossford, who somehow knows him well (?), Hayato gets an uneasy feeling.
What's more, just after the entrance ceremony, he gets asked for a duel by the campus' strongest martial arts master "Queen" Claire Harvey...!?
The ultimate academy battle begins here!


Hundred - that is the only weapon that can oppose the mysterious life form Savaga visiting the Earth. The protagonist, Kirasagi Hayato, aims to become a Martial Arts Master using this Hundred. He managed to get into the battleship university, Little Garden.
 
"I wanted to see you, Hayato!" "How do you know my name?" Around the roommate, Emil Crossford, who somehow knows him well, Hayato gets an uneasy feeling. What’s more, just after the entrance ceremony, he gets asked for a duel by the campus’ strongest martial arts master, Queen Claire Harvey.