René Simm interacts with various other characters throughout the Seraph of the End series, which affects himself and the story. This article details René's relationships with other characters.
An unpredictable seventh progenitor who is very fond of Mikaela Hyakuya. He leads the attack against Shinjuku of which René fights under his command and in the same vicinity as him.
A seventeenth progenitor serving Crowley Eusford. Currently residing in Nagoya. She fights in the attack on Shinjuku though they are not seen interacting.
A member of Ferid's political sect. Currently residing in Nagoya. He fights in the attack on Shinjuku.
Currently a city guard working with Lacus Welt and René Simm. An powerful young vampire that they deem to be arrogant. He keeps to himself. René is fine with that as long as Mika does his job properly. Ferid Bathory's favorite servant and Krul Tepes's favorite pet.
A seventeenth progenitor serving Crowley Eusford. Currently residing in Nagoya. She fights in the attack on Shinjuku.
The former vampire queen of Japan and a third progenitor. She favors Mikaela Hyakuya, and she is rumored to have turned him into a vampire. Lacus wonders if she favors him because he knows Yuichiro Hyakuya.
Currently a city guard working with Mikaela Hyakuya and René Simm. He is chatty and often attempts conversation with Mikaela, but Mika almost always blows him off. He is concerned about Mika's well-being. Lacus is almost always with René working concurrently in missions together and fighting nearby when the need arises.
A human who turns into a powerful one-winged monster. Mikaela knows him and they come in close proximity to him during the battle of Shinjuku.
The one who turned Yuichiro Hyakuya into a monster, witnessed in battle at Shinjuki. He led the human resistance at Shinjuku where they are present on the same battlefield.