Something I notice is that, if by the end of a match you've got 100 heat and you just need that one last good combo to finish them off, it's usually very beneficial to just go Blood Kain and go straight into Devoured by Darkness. Reason being, you'd be very surprised to find how little players actually know you can throw Ragna out of DbD, and who instead opt to barrier block (not knowing its unblockable properties), immediately attempt to dash away (which, depending on the situation, they might not be able to do - my favorite times are in the corner or during their pressure), or instead, having expecting you to throw out a BK combo, tried a DP (in which you'll almost always win out). Along with the nice (usually finishing if you gauge your opponent's health correctly prior to attempting) 4.4k damage you get out of it, it also nicely finishes off players who are holding their bursts for that one last combo of yours.