Izumi is a ronin from Hinomoto, user of the self-proclaimed "War God Flowing Fencing". In reality, she comes from a town of farmers, and taught herself fencing. Seems like her false personation was discovered in Hinomoto, and she ran to the continent. She came across Annelotte, and ended up following her of her own accord.
As a vain person, she won't ever say she's "just a warrior from Hinomoto" to try and correct her lie, and hates losing more than any of her comrades. She acts aloof when she talks, but she still follows Annelotte earnestly. Even if she were to lose her, she'd follow her with her full spirit. She likes to make herself seem more than she is, even trying to impersonate a ronin.
When it comes to fighting, she wields a huge nodachi (large sword across her back). She's also able to play a whistle made from seashells, that boosts her strength and her comrades'. Even though it seems as if she isn't a capable fighter, she actually is very good at fencing, which she taught herself.