The fourth sister is a muscle-brained idiot. She's dependable in the sense that she's motivated. But she worries me the most. And plus, she's... no, I'm just overthinking things. In any case, she's an idiot.
|― Fuutarou to Rena about Yotsuba, Chapter 42|
Yotsuba Nakano (
In the past, Yotsuba and her sisters used to enroll at the Black Rose Girls School, thanks to the influence of the their stepfather, Maruo Nakano. However, an unfortunate incident prompted them to transfer to another school.
Yotsuba has short, straight hair that stops just around her neck. She is portrayed to have light orange hair colour throughout Volume 1-4. Her notable accessory is a bunny ear-shaped ribbon, which can change forms depending on her emotions. Like her sisters, she has dark blue eyes, an average height, a well-endowed figure, and large breasts.
Yotsuba is an active, cheerful and easygoing girl. She talks in a loud, spontaneous and sometimes absent-minded manner. She is the type of person who can't say no to people who need help and is mostly seen helping people; either directly and indirectly.
While cheerful on the outside and towards others, Yotsuba also harbours feelings of inferiority towards her sisters and her own abilities. Her inferiority complex started to grow when she met Fuutarou when they were children and caught him talking to her sister while noticing that he did not know it wasn't her. She made several attempts to fix her complex (such as wearing her iconic ribbon and trying to excel in extra-curricular activities), which in turn made her desire to be different from her sisters. While portrayed as a bad liar early on, she is later shown to have some skill in lying herself; being able to hide her true identity to Fuutarou all the while being able to maintain their relationship, at least when together.
Knowing the Yotsuba is physically fit; she is capable of tasks that aren't normally done by her sisters. She has excellent stamina and is a good runner; meaning she has a knack for sports. Her excellent skills were shown when she scored 7.9 seconds for a 50m sprint; even getting praised by a fellow skilled club member. She is the only known sister with excellent eyesight, whilst Itsuki wears glasses, and Nino uses contacts. This definitely shows when she could see Nino's name tag from the second floor of her condominium. She even sports a good sense of smell and has a green thumb.
Like her sisters, her academic abilities are poor at best; even getting zero on a test. She is well aware of her shortcomings and even stated that she would most likely be the one to repeat a year. Ranking to be the lowest one, with her strongest subject being Japanese.
She has been noted to be terrible at lying, though she says that she could if she really wanted to. Miku and Fuutarou have been able to see through her times of deceit.
- Main Article: Yotsuba Nakano/Relationships
- "I'll support you with everything I've got!"
- "As long as you are here, there is no need to worry"
- "Do you forget that even though I'm like this, I'm still a genuine girl?"
- "I'm sorry Uesugi-san, but I can't ignore people in trouble!" 
- "There's someone, supporting an untalented girl like me"
- "In questions with five choices, chances are highest it's the fourth answer!"
- "It's because I like you"
- "If you love us, you'll just naturally be able to tell"
- "The important thing isn't where we are, it's that the five of us are together."
- "I love the view you get here when you swing as hard as you can. It's not the same as those million dollar views they talk about. But when I imagine that each of those lights is a family, it warms my heart."
- "An idiot like me can be helpful to everyone? I won't be the me who just hold everyone back anymore?" 
- "It feels like.. my efforts have been rewarded for the first time ever"
- "Even though you were an unlikable boss who always wanted what others had, you were our leader. I've always thought of you as the older sister since back then."
- "Don't feel like you should be the only one holding yourself back. Just do whatever you want to do."
- "Even you might find someone you love in the future, Uesugi-san. And when that happens, no matter who you love, no matter how you come to love them, I'll always be on your side.. supporting you with everything I've got!"
- The name Yotsuba means "four" (四) (yotsu) and "leaf" (葉) (ba).
- Yotsuba has a unique giggle: "Shi Shi Shi." This is a pun on number 4.
- Yotsuba has a shirt with the number "428" screened on it. This is a pun on her name's reading (Yo-Tsu-Ba).
- Yotsuba's voice actor, Ayane Sakura, once voiced all five girls for a television commercial for the manga in October 2017.
- It is revealed by Ichika that she still uses her panties from elementary school days.
- In the one-shot, Yotsuba has longer hair.