Serina; usually quiet and dull unless around Jin. She's always in Jin's Pocket Dimension, either doing self training or watching Jin's adventure through the television.
With 57 Determination souls fused together, she's able to manipulate structures and her surroundings from sheer will and can create a variety of weapons to aid her in battle in a huge amount. She can also persist death many times.
Savant; a psychopathic being that bears Jin's memories and stolen negative emotions from his past and current life with the corrupted Determination combined. Now getting hold of a body they can use, he goes from timelines from timelines to slowly accumulate determination souls to transform them into strange powers using a method similar to the combinings of souls that created Serina.
He is also the reason why the story gets a sudden turns of event, due to being aware, just like Jin. Without his intervention, the story would've gone the usual route where Jin stayed as his killer sans form thoughout the story.