Vissarion

While Vissarion's availability isn't until late game, his passive and class tree is so strong that he will almost be an essential unit in your Demonic playthrough and you will be wondering how you've made it this far without him. Able to buff a fragile unit like Tal'Dera into a unit with decent bulk is something that only Vissarion can do. Vissarion's personal skill could be argued to S tier as he can make already tanky units undamageable; however, I believe that A tier units belong where they do because they require mana batteries to really make them pop off as you're not going to have the mana to use your buffs every turn. 

At level 30, you generally have about 10 more levels to go. Unless you are favoring a character or farming a lot, You generally won't make it much past level 40 - MAYBE level 45. At this point in the game, look at the character's bases compared to the growth rates. For every 10% of a growth rate, just add 1 point and you'll have your level 40 endgame stats. 

Vissarion is one of the better units in the game. His personal skill will make or break your tanks in Demonic. Other than that, he's another super buffer like Gwen and Valeria. For that reason, I simply cannot justify putting him in Ancarant or Champion - even though he can perform those roles, he would rather buff his team and either grab objectives as a Reaper or pick off a threat from the rear as an Ellisant. 

Reaper - Standard Reaper build. Gallant for tier 2. The Greataxe is perfect if you can fix the accuracy problems, Destiny Ring for guaranteed crit, Lava/Mystic/Heir Ring for boosted buffs. Pump mana in him and let him buff. 

Ellisant - Standard Ellisant build. Nightblade goes hard for a tier 2. Any bow with Ferocity Rune. Lava/Mystic/Heir Rings + 1 of your choice. Vissarion makes a great unit to equip a Lava/Mystic + Heir Ring with his high HP that you can Elixir up to max out Heir Ring. Double dipping makes for some insane stat buffs; however, is often overkill. You will definitely need to feed this man some mana!