The Red String of Fate.

a bond ties the two together to a spiritual level, the bond can never be broken from normal means, if two players take this feat they are,

immune to charming.

one always knows where the other is if they are at least 100ft apart.

gain advantages on any checks involving the couple. (the advantage gained can't be use to attack enemies normally but can be used to save the other person that has the shared bond)

any illusion or trick involving the couple can immediately be seen through.

can perform a instant reaction to save the other in question, if they are within 10f of each other. (IE: enemy attacks person 1, person 2 can react to block the attack or save someone from a trap. if the roll to save the other person fails the user can take the hit instead of the other person)

with both players that take this feat. if one player uses a charisma check on the other player that player always has disadvantage.