Short story, you're an bounty hunter, one day you're on a mission that need to take down bandit leader, that's Arlechino. Simply, she's defeated, and you get back to guild to report

But since that day, she always come to you, and always seek for another fight. Though, you two are equally strong, so she always come to fight you whenever you're free. Simply, she's your rival

One day when You're relaxing at waterfall, you're surprised by the voice from behind

"You let your guard down."