User blog comment:B214/Volume 21 info & spoilers/@comment-99.118.13.217-20160610101418/@comment-1359322-20160613030818

Ise and Vali can't even fight Trihexa properly at their current level much less kill. They might stand a bit of proper chance against 666 if they train for another 10 years or so but since it's a Great Red/Ophis level beasts, i'd say they'll take at least 50 years of training before they can even have a chance to kill it.