A robot girl who was built by Hakase and lives with her and Sakamoto, acting as the matron of the house. Hakase is constantly upgrading her against her will, and Nano worries this will betray the fact that she is a robot, despite the presence of the obvious metal key in her back.
A bright and cheerful girl sporting azure-blue hair and pigtails held by two small wooden cubes. She is more 'normal' in contrast to her friends Yuuko and Mai, though she has a very short temper and is prone to tantrums. She has a crush on Kojiro. Mio is smart and excels in academics, and Yuuko often copies her homework. She likes to draw yaoi in her notebooks but is mortified of it being discovered, often displaying unhuman strength when trying to hide it. (Source: Nichijou Wikia, edited)
Asura's weapon. It was devoured by it's own master, Asura, after becoming a Kishin.
Otama Jackson is a gigantic black tadpole with googly eyes, a long tail and a wide red-lipped mouth bearing a set of sharp teeth. He is a very loyal and hard-working familiar, always doing his best to serve Eruka, even if it means putting himself in harm's way. His main function is to act as a mount for Eruka, using his large size and capability to fly to aid his master in whatever way possible. However, Otama Jackson has very low stamina, and cannot fight at all, making him easily exhausted and extremely vulnerable to attack. Unlike other Witches with their familiars the two seem to share a close friendship with each other despite Eruka's apparent dominant role in the relationship, with even the normally docile Eruka reprimanding Free after he only slightly injures Jackson. Jackson in turn is extremely loyal to Eruka, going so far as to help pass her the needle of Black Blood that is supposed to reawaken Asura before Black Star can get at it, resulting in the tadpole getting beaten up by Black Star. Eruka laments over this, and decides to fulfill the mission solely for Jackson's sake.
The Succubus is a demon who has adopted a female form in order to seduce men so as to absorb their life energy. She currently resides in the first chapter (Lust) of the Book of Eibon, after an unsuccessful confrontation with Noah resulted in both her permanent imprisonment and addition to his collection. In a further attempt to attract men in addition to her rampantly seductive appearance, the Succubus conducts her movements in the most perverted way to expertly accentuate the most bewitching and attractive aspects of her female form. Befitting her need to entice men in order to fulfill her respective desires and vice, this particular demon has assumed an alluring form that she believes best caters to a typical man's wants: A young and voluptuous female with an ample bust. Her softened facial features are contrasted by the stark addition of a vertical line descending from either of her eyes (Which are shown with heart shaped pupils); these lines are connected by a horizontal line that runs over the bridge of her nose, together creating an "H"-shaped marking. The rest of her face is concealed beneath a layered and spiky hood, featuring two prominent horns protruding from the sides. Further placing emphasis on her seductive qualities, the Succubus wears the bare minimum of clothing; consisting simply of skintight gloves and stockings decorated with "H"-shaped accents at their openings and a revealing apron that exposes the majority of her back, except for where a few small strands keep it attached to her body. This wardrobe choice's open back also prominenty displays a "certain aspect" of her appearance. A small, slightly coiled devil-like tail extends from just below the small of her back. The numerous "H"s on the Succubus' person are most likely a reference to the Japanese word ecchi, denoting sexually explicit material or behavior; "ecchi" is a spelling-out of the Japanese pronunciation of the letter H, and could have originated as a polite codeword for hentai in the 1960's.
Wes Evans (ウェス・エヴァンス, Wesu Evansu) is Soul's brother and was the first one to find out about Soul's weapon abilities. He is said to be a master at the violin. Soul feels that he can never be like his brother because he does not know what he is 'capable of'. In the manga, Wes and Soul look exactly alike except for the age difference and how Wes's hair is more tamed than Soul's. (Source: Soul Eater Wikia)
Former pirate captain, now the owner of the sea restaurant Baratie. He is the person who raised Sanji and taught him how to fight and to cook.