Kingdom may have had some sprinkle of supernatural but no one ECER thought we would be getting into the realm in Kingdom to revive characters or touch the revival concept, I don't care what anyone says about Shin being revived, that was bullshit, fairy tail/dbz tier writing. How about not kill the character at all?
Well now the discussion seems to have changed from the presence of the supernatural in Kingdom in general to your problem with one specific supernatural moment in particular. Lol.
Anyway;
I) Directly interacting with and flat out talking to spirits is not a sprinkle of supernatural, that is flat out, full on supernatural. There is no two ways about it.
II) I never read Fairy Tail but I have read/watched DBZ and I do not see what comparison you are trying to make there. The revival element of DBZ was clear cut, explained and involved the central plot point of the series (i.e. the Dragon Balls).
Likewise, the stuff involved in the Red Stairway plot point was set up way in advance. Ki was explicitly talked about in Chapter 85, Kyoukai entire fighting style revolves around this ki and the exact technique used was alluded to earlier in the arc, dozens of chapters in advance.
III) "How about not kill the character at all?"
Well that depends on how the Red Stairway plotline ends because it still has not done so yet. This plotline will end when the consequences to Kyoukai are finalised. If what I expect comes to fruition then this plotline was more about Kyoukai than it was about Shin.
Some of my speculation on these consequences.
https://worstgen.alwaysdata.net/for...ap-between-heaven-and-earth.2915/#post-230955
https://worstgen.alwaysdata.net/for...ap-between-heaven-and-earth.2915/#post-231722
Even if this does not happen, the Red Stairway plotline is just an extension of Kingdom's already long established spiritual elements.