some time ago I was interested in how people actually no hit sekhema without 1000+ hours of practice runs with simulate 1hp (eldritch battery + chaos inaculation, btw thats the way to go and practice for you)
so i found some old comment here about build just for that, with realy interesting mechanics used
its hard to remember everything correctly, but what you need is temp chains with as much magnitude as it can be, casted on yourself, and two hammers that every 10 sec give you random, non-damaging shrine buff
then you wait until divine shrine buff (invulnerability one) is given to you, and because you cast temp chains on yourself, as said in temp chains skill - effects expire slower on you - so you will have like 30+ seconds of invulnerability this way, so there you go, just need to time it right