Parabatai rune

A rune that partners two Shadowhunters together, so they can draw on each other's strength.

Know people with Parabatai rune
Jonathan Shadowhunter and David the Silent (split by David's Silent Brotherhood)
Silas Pangborn and Eloisa Ravenscar (split by Silas' death)
Jem Carstairs and Will Herondale (split by Jem's Silent Brotherhood and Will's death)
James Herondale and Matthew Fairchild
Cordelia Carstairs and Lucie Herondale
Michael Wayland and Robert Lightwood (split by Robert's exile and Michael's death)
Valentine Morgenstern and Lucian Graymark (split by Luke's Downworld transformation)
Jace Herondale and Alec Lightwood
Edward Longford and his unnamed parabatai (split by the latter's Turn into an Endarkened)
Julian Blackthorn and Emma Carstairs