If you have bonded Cassandra with Riordan/Alden and Saxon with Valeria, you should have enough gems to make the Sanctified, Bloodied and Victorious Rings. If not, getting the objectives may be much more difficult on demonic and you may just opt to skip it altogether. Alternatively, you can also just accept the shrine on last turn as long as you can take a hit.
Ideal classes: Gwen: Seeker with Colossal Longbow (effectively 0 speed on linear levels until level 19 - super important)
*Arthur: Scholar (Ancient Writ mana cost is nice early on)
*Alden: Aegis (Repulsor Shield turn extension - super important)
Saxon: Monk (charged ki meets speed check/decent uptime)
Valeria: Nightblade (speed)
Cassandra: Waveseer (debuff cleanse on healing wave is very nice for demonic)
Riordan: Quickdraw/Cuttthroat - Quickdraw generally better player phase combat, Cuttthroat for Licky Lasso.
*personal preference of who is what. Alden is generally better for Aegis; however, you can wait to change him until later when you hit the training maps.
Strategy for Demonic:
With the victorious ring and the colossal longbow, you can have Gwen get doubled by everything with 5 speed or more. (Trees are generally about 4 speed, so do be careful.) If Gwen kills something, she procs her passive giving her light block of up to 15. Gwen has decent bulk so she should be able to survive the first hit and maybe die to the second. If you keep 4 stacks of Repulsor Shield (R.S.) on her (feed mana to your Aegis with Scholar's Ancient Writ) and let her get doubled, this will kill the enemy. As long as you have Victorious ring equipped, she will proc the 20% heal, and she will come back to life as if she never died. Additionally, killing something with R.S. also procs her passive.
So as long as you have enough bulk to survive the first hit with her light block stacks, you can infinitely loop this.
If you don't have the Victorious Ring, just hunker down. Khamari is very tanky and can be put in a choke point 2 spaces ahead of where Benji starts - just remember to use his "Transfusion" skill and have your Scholar use Ancient Writ on him so he can use it often. Bloodied Ring should also be utilized to make sure a unit isn't doubled or can double and ORKO something.
At this point, the shop offers:
several Astral Coins (5-6 depending if you bought any before)
Sapphire x1 4000G
Elixir of Might x1 5000G
Don't worry if you can't afford everything. These items will persist until you buy them.
Objectives:
Dagger Rune x1
Sword Rune x1
Chests:
None
Enemies:
Astral Coin x2
Life Essence x2
Axe x1
Gold x2000
Emerald x1