Hand Shakers are teams of two people fighting other pairs of Hand Shakers for the right to battle god. When a Hand Shaker pair loses the latter continues to fight while the losing team loses the ability to summon their Nimrod and their position as Hand Shakers are nullified. Hand Shakers generally appeal to having code names and team names. Such as Tazuna and Koyori are Team Gear, Chizuru and Hayate are Team Shadow, Break and Bind are Team Chain and Riri and Masaru are Team Card. Generally each pair have a wish determined to fight god. Team Gear's wish is Determination, Team Card's wish is Love, Team Shadow's wish is Ideal and Team Chain's wish is Kindness.
How to become a Hand Shaker
How hand shakers generally become a pair is when they have connecting emotions and a powerful bond. Each hand shaker pair is shown to be very deep in their bonds and have backstory together.
Hand Shakers may be separated if their deep bond is broken. An example would be Makihara and Nagaoka.