These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Arc Fatigue: The Death Zero arc. All the arc is a huge Secret Test of Character from Hao to Hana, in order to teach him that being strong is more than reckless strenght, fighting must be done with a purpose and to get him a brand new spirit partner. The whole arc happens inside the Great Spirits, most precisely, Hell; but people are getting tired of the slow progress and really want to know what are doing the living members of Team Hao right now.
Author's Saving Throw: Hao being a massive Karma Houdini in the original series is addressed with the revelation that he's not Easily Forgiven and many of the previous Shaman Kings are understandably not pleased with a mass murderer like him in that position.
Fridge Brilliance: Hana has more power than his father Yoh had at his age. Considering that Hana died as a baby, dying is the best way to increase furyoku (spiritual power) and we don't know how much time passed before Hao revive him, is understandable.