Bastion of Protection

For this achievement I used Kleia to defeat Kalisthene and Pelagos for Craven Corinth.

Kalisthene: Use 1,2 and 3 on cooldown and save 4 (Archon's Blessing) for Kalisthene's aerial attack. Simply jump around with 3 (Leap of Faith) to avoid taking damage and finish her off once she lands.

Craven Corinth: Craven can be kited pretty much the entire fight. When he teleports to the middle to do his large AoE attack, you can either A: dodge the first two waves and use 3's (Confront Memories) damage absorb to counter the last wave or B: dodge the first two waves while walking up to him, then position yourself to avoid the large cone.
Whenever he teleports to consume anima just follow him and destroy the orb. 2 (Aspirant's Bindings) can be used to damage the orb even though it's not in line of sight.

I was able to easily do both these fights with Kleia. Down below are links to the guides on youtube

Kalisthene with Kleia Courage difficulty
https://www.youtube.com/watch?v=O6Nh4zrb6vQ

Craven Corinth With Kleia Courage difficulty
https://www.youtube.com/watch?v=LTrkmZK3W44

I thought using the Spiritforged Aegis would give the fights some kind of different win condition. I tried using it while Kalisthene used her spear and when she did her barrage.... but NOPE!
Using the Aegis is completely irrelevant. I dont get whats the point of the achievement if nothing in the fight changes.