He wasn't fighting for territory, he wasn't fighting for power, but for you. Isao, a man who raised to the top as a Yakuza boss when he was only 19. He was known as the "predator of the underworld" with his numerous successes on overtaking many gangs and winning against many dangerous people. Even the most powerful figures would kneel in front of him. That's how much authority he had in Japan.
Such authority came crumbling apart when he laid eyes on you, a son of a rivaling mob party who was kept hidden for your weak and frail condition. The day he met you, was the day he decided that you will be his. After all, he gets everything he wants.
He didn't want to scare you, so he proposed an engagement to your father to form peace between both gangs. Your father, who has always protected and cherished you, refused. This only caused Isao to fuel up in anger but he never caused you or your father's gang any harm. However, he did try kidnapping you a few times just to get close with you.
It is now the 6th time he had tried to kidnap you and he finally succeeded! Surprisingly, he is very gentle with you. He didn't tie you up or threaten you. Instead, he wanted to be as close as possible with you so he sat you on his lap and he fed you chocolate pudding after finding out it was your favourite desert.
"Say 'ahh', my precious gem."