Once you give your energy to other creature and that creature gives you energy back, your energies unite and you're becoming one with them. The energy exchange becomes continuous. Giving purifies the energy quality. Untimely bringing both creatures to the state of bliss. But it only works on the close distance, proportional to the united energy capacity of both creatures.
From that moment a thread on love and friendship will unite you together.
At any moment, even if they're not close, you can ask them for energy. For example in the middle of the battle when facing a dark creature with higher energy capacity.
Not being here and now.
Being one with creatures, which are not here and now, or not giving the energy back, causes pain. And creature might even die dwelling on something happening in the past/future, or wanting to be with someone who's not here or not wanting to be one with you.