Real fighter

I did not quite believe this was a real fighter betta when i first bought it. I decided to let it fight with a 30% bigger betta for a try. He was first attacked by the opponent for more than 10 times, then it fought back. he liked to bite the opponent's fin and dragged the opponent down to the bottom. I stopped the fight after 20 minutes when both bettas looked tired. Sadly, the opponent died on the next day.