When they met, Shido thought that Marina was another personality of Maria that appeared during nightime. However, he finds that this "Arusu" was ruthless, to the point of deleting Tonomachi's NPC on a whim. After several repetitions, Shido witnesses Marina helping an old woman across the street, and he congratulates her for this. Later, he shares a meat bun with her. At the end, Marina thinks she's going crazy due to her actions, but disappears with a smile on her face when Shido tells her that she was not really bad; she was just a blunt person. At the end of her route in Rio Reincarnation, after gaining Eden's power from Rio, she confessed her love to him.
When Marina entered the Fraxinus, the AI copied her appearance, thus creating the girl known as Maria Arusu. Marina came to hate Maria, to the point of telling Shido not to compare her to that copy. After Marina is weakened during the final battle, she and Maria exchange their memories with each other, allowing them to come to terms with each other.
When they first met, Marina saw Rio walking and trying to find something important. She decided to help her to find "The most important thing", because she, along with Maria were concerned if anything happened to Rio during her search.
Isaac is the one who created Marina and is also the one who gave her a name. She was programmed by him to watch over the <Ratatoskr> by hacking its program. In the true route, she called Isaac as "Otou-sama" (or "Dear father" in English), showing that she is very loyal to him until the very end.