Syn Link

Syn Link (シンリンク; Shin Rinku) is a Lost Magic, a very powerful subspecies of Organic Link which creates, or, it is more correct, gives manifest form to profound bound between two people and allows them to connect their magic to each other.

Trivia
Syn Link derives from the Greek prefix syn, which mean "with, in company with, together with". It is the root from the English word sympathy.