Shoujo wa Isekai de "Satsuriku no Sainou" ni Mezameru

Hikaru is a high school girl who is seriously injured by bullies and loses consciousness. When she wakes up, she's in a coliseum in another world as a sacrifice! Then, Hikaru awakens to the "talent for slaughter" that she had trapped deep inside her heart, which she never had a chance to use in her peaceful country.

(Source: Champion Cross, translated)