Dependence on limited items, a lack of things to purify... Good game design.
Thank God most people are complaining about it and giving the devs appropriate feedback.
Ok, "limited" items (you'll eventually be able to get loads of them, potentially unlimited) aren't good enough for you?
Try Yokai Core abilities. These are upgraded in the Dark Realm, and several of them are good at smacking around the boss's Ki bar, which, in case you didn't know, forces the boss out of Dark Realm if you break his Ki. Additionally, these can be used while you are out of Ki, basically making them exceptionally useful for getting out of binds or recovering from running out of Ki, and you generate extra Anima in the Dark Realm to fuel them.
Try Yokai Shifts. These will let you wail on the boss. Might not be as strong as Living Weapon was, but it's way better than nothing. Also usable when out of Ki, making it a get out of death free card.
Try looking at the Shiftling and Omnyo trees. Both have easy to reach *PASSIVE* skills that enhance your ability to resist other realms. Omnyo gets +10 resist to other realms, and Shiftling gets up to 30% reduction in ki penalty while in Yokai / Dark Realm. Both are very early on in their respective trees, and are always active, so anyone can pick it up.
Try Ki Flux. Get used to tapping the button to recover a large portion of your used Ki after every combo. Reduced ki generation does nothing if you keep recovering your lost Ki anyway.