Depends entirely on what drawing on each other's power entails.
Basically, I'm trying to create something similar to the vampire marks from Anita Blake, only less strong and without all the crazy sex stuff that accompanies them, and also making getting the marks more interesting than just "vampire gives them to you."
My idea is that I'm creating a dhampir (defined here as a being created when a pregnant woman is Turned into a blampire--when she gives birth, the child is a dhampir) who is something like a cross between Jean-Claude from Anita Blake and Stefan from the Mercy Thomson series. The way dhampirs work in this story is that, so long as their mother is still alive, they are forced to obey the master vampire that turned her (non-master blampires can't create dhampirs) and dhampirs have a limited amount of supernatural ability (inhuman powers and maybe a negligible amount of magic, basically) but if they kill the master that created them, they 'unlock' the ability to develop their powers further (the idea for this comes from a WoJ that blampires gain power by killing people). Also, because their natures are so unbalanced in favor of death and darkness, all dhampirs are drawn to sunlight, despite the fact that it kills them.
This dhampir is no longer obligated to obey his master, but that master is still alive. So this dhampir decides to convince my character to trust him (via asking for help with stuff my character would want to get involved in, offering his help to her practically free of charge, and generally being nice and helpful) in order to manipulate/convince her to perform a ritual that would give him both an ally and more power in order to kill his master, and also would allow him to walk in sunlight, to some extent.
In the course of this, they become friends, and they end up binding themselves together with the five elemental Marks, for various reasons.
The Water Mark is placed by the dhampir/vampire sending his energy into a person, causing some of their energy to flow back into him. This has a mild healing effect when it happens, but not long-term. Without this or the Earth Mark, however, the other Marks cannot be taken.
The Earth Mark is an exchange of blood between the vampire/dhampir and a person. This allows the person to keep functioning for a scene even if they are badly injured (basically, it works similarly to Harry's bear belt buckle).
The Air Mark is triggered by looking into the vampire/dhampir's eyes--which normally allows a blampire or a dhampir access to your mind, and is sort of like them having your Name in terms of problems blocking it--and having the will to take control of the connection and reach back rather than succumbing or breaking the link. This allows the dhampir/vampire and the person to speak mentally when they are close to each other or in each other's dreams.
The Fire Mark is triggered by the vampire/dhampir allowing a person to pour faith magic into them and accepting it (essentially allowing themselves to be taken out) and allows both of them to know when the other is lying to them, and allows them to sense extremely strong emotions in the other.
The Spirit Mark is triggered by the vampire/dhampir jointly casting a (strong) spell together, and can only be taken by someone who has at least one of the Earth/Water Marks and at least one of the Air/Fire Marks. It allows either of them to be able to find the other no matter where they are (if you're too far away, you may only get a vague direction, but you can follow that to get closer).
When someone has taken all five Marks, they can draw on the vampire/dhampir's power, and the vampire/dhampir can draw on theirs. What this means for the living person is that if the vampire/dhampir has supernatural speed and/or strength, the person can draw on the inhuman version of one of those (but not both at once, and you can't switch mid-scene); can draw on any spellcasting abilities that the dhampir/vampire might have, but with an effect like Demonic Co-Pilot; and can gain shifts for necromantic spells by inflicting physical stress or consequences on the vampire/dhampir if they don't resist. What this means for the vampire/dhampir is that they can heal themselves by drawing energy from the person (inflicting physical stress, or optionally mental if the person is a spellcaster)--the person cannot resist this, which can be a problem in a fight; can draw on any spellcasting abilities that the person may have (or possibly other supernatural powers, if they have those); and gains armor:1 or 2 (I don't know which it should be yet) against any attacks made with their Catch.
