I don´t know, i still read the series but all those weird monsters appearing (which is apparently the manifestation of their spirits if i understood it correctly) kind of disappointed me. I preferred the series primarily being a martial arts series.
I suppose that could be true for a lot of people too. It started out close to a martial arts series but there were signs in the first chapters that something else was up when an island was destroyed and people thought it was some new weapon.
I feel like a ton of martial arts series end up with crazy powers anyways unless they are based around a sport like boxing.
Strangely enough those spirits remind kind of "Shaman King". Wristbands with powerlevels, the whole series centers around a tournament, the main rival having some insane ancient power, and the winner of the tournament get unbelievable power.