The fourth volume of To Your Eternity features Gugu and Rynn on the cover. On the back of this volume is a silhouette of Tonari.
Four years dedicated to his family have molded Fushi into an approximation of a human. But Fushi's new acquisitions in that low-stimulus life have been few. When he attends Rynn's birthday party, Fushi is attacked by a Knocker. Can Fushi, fighting with the help of his brother Gugu, defeat the Knocker and defend his family? This is a story of turning pain into strength.
- Chapter 25: Winding Road (まがりみち)
- Chapter 26: Crossroads (わかれみち)
- Chapter 27: Gift from the Past (過去からの贈り物)
- Chapter 28: The Megalith which Rends the Earth (大地割る巨石)
- Chapter 29: The End of the Mask (仮面の最期)
- Chapter 30: The Family on the Hill (丘の上の一家)
- Chapter 31: Awakening (目覚め)
- Chapter 32: Straying Path (惑う旅路)
- Chapter 33: Will Toward a Higher State (高みへの意志)
- Chapter 34: Isolated Land of Death (閉ざされた死地)
- In an interview with Oima Yoshitoki, Oima said that each volume cover depicts a character's dream. Gugu's dream is to live without wearing a mask and to protect the people he cares about, so volume 4 shows Gugu, without his mask, protecting Rynn.