Besure to check out Smis Liu Ishmael video of soloing 5-30, it is much more epic to use Liu Ishmael instead of easier R Ishmael
For R Ishmael, it is mostly pray that the enemies on wave 1 don't roll too much head and stagger you
Once you get to turn 4, you should be good to go as you could start healing back up using Gregor support passive
Then use the rest of wave 1 and wave 2 to heal up and stock up mind whip
Remember to have enough charge for 2 mind whip before getting to wave 3
Preferably, you could use 2 mind whip on wave 1/2 so you could get 2 wrath to use the base EGO to clash his third skill
Once he use the Test of The Big Brother, throw everything you have to him on the following 2 turns while try to stagger little brother on the first turn his gimmick debuff on
Be careful as both little brother 2 coin skills can potentially out clash your skill 1
0:08 Wave 1
5:53 Wave 2
8:14 Wave 3