sometimes I just don't get why people make villains like this. The MC has too much connection to the demon hunting crew to kill them, and this is a shounen, so there is absolutely no way in hell they are losing this. On the other hand, it's the MCs sister-turned evil, so you can't kill her either, so the obvious option is to either befriend her, capture her, or kill or force all of her friends to retreat. On the other hand, shounen logic might dictate that since she has a direct relationship to the MC and he doesnt hate her, she might be just fighting them because the captains were getting too close to her brother and might secretly be infiltrating the shuuki to do something to them from the inside, either that, or she might be "possessed by an evil energy".
tl;dr this is a shounen, the author probably wont kill any of the humanoids and the demon hunting crew will probably just capture the shuuki riders or something, or force them to retreat, or some of both