The Ring of Mylinn is a magical item featured in Valkyrie Profile 2: Silmeria which appears to stop the passage of time for its user. It is lozenge-shaped and set with a distinctive red gem.
The ring's primary usage in the game is to preserve Rufus' body. Since he is the only half-elf in existence besides Odin, the latter wishes to have him at his disposal as a replacement vessel, and thus needs to keep him in optimal physical condition. The ring prevents his body from ageing or dying, and he cannot remove it, as he has been told that it would cause his soul to burn away . This also means that he is unable to be reborn.
When Alicia encounters Rufus in Solde, Silmeria spots the ring on his finger and prompts her to enlist his help for their journey to Dipan. This indicates that Silmeria is aware of the ring's function and would therefore be able to recognize its bearer as Odin's replacement vessel. Later on, in Chapter 3, Leone has a similar reaction.
The ring's significance is revealed in Audoula Temple on the Lake when, after battling the guardian of the Temple's dais, Rufus inadvertently comes into contact with the latter. This causes a reaction which flings him to the ground, the ring falling off his finger in the process. This immediately causes him pain, and Silmeria instructs Dylan to put the ring back on his finger. Rufus then reveals his real identity, as well as the fact that he has a personal stake in Silmeria's endeavour: if they manage to defeat Odin, he might be free to live his own life.
The ring is later used for a different purpose. After Dipan's destruction and Silmeria's kidnapping by Lezard, Alicia and Rufus decide to challenge Odin themselves and travel to the Forest of Spirits to attempt to cross Bifrost, the rainbow bridge, into Asgard. However, humans cannot access the bridge, and the pair is forced to rethink their strategy. Roussalier, a sympathetic elf (usually thought to be Rufus' mother) who saves them from Heimdall, the guardian of Bifrost, mentions that the only way for a human to cross the bridge would be to become an Einherjar or an undead. This gives Alicia the idea to search for Ghoul Powder in the laboratory of the Three Mages of Dipan, as they have used some to become undead themselves. Rufus then suggests that she wear the Ring of Mylinn while they cross Bifrost to halt the transformation, so that it only affects her body, but not her mind. Once they reach Asgard, neither of them will need the ring, as time does not flow there. Their scheme is successful, even though Rufus becomes temporarily vulnerable while they cross the caverns that lead to the entrance of Bifrost.
Once in Asgard, the pair sets off for the top of Yggdrasil, where the knowledge of the gods is said to be contained. As they are resting during their ascent, Rufus sees the ring still on Alicia's finger and suggests that she take it off, since she does not need it anymore. However, she now perceives it as a symbol of her affection for him and says that it has become her good-luck charm. She then kisses the ring, which causes Rufus to become deeply embarrassed, fibbing that the ring is too big for her and looks silly.
The ring is then used to materialize Rufus after he is fatally wounded by Odin at the top of Yggdrasil. His soul is displaced by Lezard, who has been following the pair in the hopes of reaching Odin. He transfers Odin's soul into Rufus' body, steals Gungnir and disappears. Alicia then manages to absorb Rufus' soul, but in order to perform the materialization, she needs to concentrate on an object that belonged to him, and the Ring of Mylinn has fallen off her finger during the confrontation. She sets off to find it and finally manages to materialize Rufus, who then comments that the ring does not look so silly on her anymore.
After Alicia has fused with the souls of Hrist, Lenneth and Silmeria to create the one true Valkyrie to confront Lezard, the latter stabs her with Gungnir before his soul dissipates. This causes the four souls which form Valkyrie to start dissipating as well, but when an anguished Rufus calls out to Alicia, her soul takes control of Valkyrie's body one last time to kiss the Ring of Mylinn, which is still on her finger, as a form of goodbye. Rufus then keeps the ring in memory of Alicia.
Later on, Rufus meets a reincarnated Alicia as a child in Coriander. She trips in front of him, and after he helps her up and sees her on her way, he kisses the ring, much as she did before she vanished. This prompts the little girl to turn around, but Rufus has already disappeared.
It is unknown whether Odin had any other potential replacement vessels before Rufus, and it is therefore uncertain when the ring was created or by whom (by the elves or by the Aesir). It is not even certain that this was the ring's primary purpose.