Lifemate

A rough and tumble species, Sirens do not do anything half-measure. This includes mating, where they will leave literal marks on their partners. A Lifemate, and the Lifemate ceremony, are another example of how the Sirens refuse to do anything half-heartedly. A Lifemate is the person you wish to spend the rest of your life with. The ceremony is seen as a formality within the species, but a necessity for interspecies relationships.

Execution

An official Lifemate ceremony is a simple but sacred occasion. Blood is seen as precious, a necessity for life. Shedding and taking blood is incredibly symbolic. When it is done between two partners it is a way to signify the bond between them. Small vials are filled with the couple's blood, and then they are traded and consumed.
In an unofficial setting, Sirens will simply draw their partner's blood and drink from it. There's no need for a ceremony when you're already biting each other.
These ceremonies, official or otherwise, are also where a couple may discover that they are Bonded.

Components and tools

Blood - always necessary

Participants

The couple is always the most important, and they do all the heavy lifting themselves. A ceremony can be limited to just the couple and the officiator, who oversees the filling of vials and the trading of blood. During a ceremony between a Siren and someone not of their species, it is usually expected that the non-Siren will have a parent, close friend, or other guidance figure in their life present. In these situations there is an overseer, but it is the Siren's responsibility to attend to their partner and coach them through the process.