Divine Beasts (The Legend of Zelda: Breath of the Wild)
Through a curse, Lothric and Lorian (Dark Souls III) possess a connection that bonds their very souls to one another…
…their souls becoming inseperable even in death.
Lord Voldemort (Harry Potter) holds a strong telepathic connection with Harry and Nagini, as they both contain fragments of his soul.
Nagini (Harry Potter)
Through a process called "Soul Resonance", Weapons and their Meisters (Soul Eater) are able to connect their souls with one another, amplifying their power off of one another and accomplishing amazing feats.
The Machine (Amnesia: A Machine for Pigs) holds a fractured piece of Oswald Mandus' soul. Because of this, should Oswald die, so would the Machine.
Snow and Koyuki (Marchen Awakens Romance) are connected because Snow was created from a fragment of Koyuki's soul.
Charlotte "Big Mom" Linlin (One Piece) used her own soul to create Zeus, Prometheus & Napoleon, thus she can freely summon them to battle at any time.