Yomi's power is mostly singular. She has a limited ability to control and contain the energy that makes things live. The most important limitation is that she cannot control the life energy in other living beings, unless those beings have, at some point, been dead or have submitted to the manipulation voluntairily. She can, however, contain as much as she can get her hands on, and can drain very small ambient quantities out of the air with a somewhat time-consuming ritual. She can put it to as many uses as she can come up with. She can create small, temporary beings out of it, capable of carrying small objects or perhaps delivering a short message. She can imbue others with it, causing them to regenerate or heal rapidly, capable of sustaining those near death, but re-growing limbs, etc. requires both excessive energy and a lot of time. She can put it to a large number of uses internally, for example, she can use it to deny physical needs and such, like sleep (which she is quite fond of doing, due to the price that accompanies her power), breathing, etc. and has demonstrated the ability to drink copious amounts of alchohol as she negates poison with it as well (The more dangerous the poison, the more energy it takes). She can also heal herself and manifest low levels of superhuman physical ability.
She can also sense "2nd (or more) lifers" at about sight range.
She also carries an incredibly durable, heavy book on her person at all times, though where on her person is not entirely certain. This book functions as her 'Bible' as well as a sort of arcane tomb for any sort of more... Esoteric uses one might imagine for her ability. In theory she may be capable of appealing to whatever force she worships for some form of... Uhm... Death intervention, but I suspect that requires substantial sacrifice and is not something to be done lightly... If ever.
Her power is greatly derived from her faith and doctrine which she follows closely, and aside from her limited pool of energy to draw on, she also must live through, in her dreams, the lives of those 2nd (or more) lifers she absorbs fully (Or, I suppose, if anyone ever chose to donate all of their life energy to her she'd have to live out their life too...) since their most recent ressurection until the time she destroyed them.