Kenjirou is itsuki’s editor and may God bless him for his efforts. He spends a good deal of time trying to keep his writer on track to meet his deadlines. He has the skill of a great detective, tracking his often-elusive author to the ends of the earth, when he is on a “research” trip. We use quotes because “research” is often Itsuki’s code for procrastinating. Kenjirou, whose desk is piled with manuscripts and inbox is flooded with messages, actually has his act together. He plays the role of disciplinarian and devoted fan, admitting that he loves reading Itsuki’s books before anyone else gets the chance. We think finding a career you love, putting up with all the crap that can happen and still have a great attitude about it is part of having it together.

Miyako met Itsuki in their first year of college when they sat next to each other. Her first impression of him wasn’t great. The two eventually hit it off and become friends. She also seems to be his only friend and is one of the people he first tells of his debut as an author and that he was quitting school. She is one of the few characters in the series that doesn’t have a direct connection with publishing. She seems to have a crush on Itsuki, something he doesn’t realize or is just ignoring, baka, because she’s really cute. She does give him unwavering support and enjoys reading his work.

Miyako is one of the few characters that has their act together despite still being in college. Her biggest problem is her lack of honesty with herself and Itsuki. She seems to have had a crush on him since they first met in college and has yet to act on it. She may not have it all together but she’s about 90% there.

Setsuna is a talented illustrator and has done the art for Itsuki’s novels. Itsuki fired him not because the art was bad, but because the writer thought his novels weren’t good enough for the art. He is a rather easygoing artist who seems to float from job to job, but he puts his all in for each of his works. Like a lot of laid-back artists, Setsuna seems to have it together because he doesn’t put any undue pressure on himself that doesn’t involve his artwork. He is challenged at one point to draw a manga and concedes that his art was brilliant he but couldn’t tell a story like an experienced manga artist. We think part of having it all together is knowing you still have a lot to learn.

Kaiko is the manga artist chosen to adapt Itsuki’s light novel series into a manga. She is uniquely qualified as an artist for the adaption of the series as she is a huge fan of Itsuki’s and a fellow siscon. Like most of the characters in the series, Keiko has an odd quirk or two, siscon notwithstanding. She has an underwear fetish, a point she clashes with Itsuki about since he prefers that his characters not have underwear in the reveal scenes and she deems it important. Kaiko goes to the extreme of showing that when she unwraps the bow on her head it is indeed a pair of frilly panties (the show even uses a title card to explain how they were folded). We don’t get to know Kaiko very well in the course of the series. We can tell that she may have a screw or two loose given her fetishes, leading us to believe that she probably has a few other flaws as she tries to get her life together.

Chihiro Hashima is Itsuki’s younger step sibling. Because he didn’t support his father’s remarriage, Itsuki never payed Chihiro any mind to the extent of not even realizing that this new sibling was indeed a girl and not a boy as he assumed. It wasn’t until Isuki moved out that Chihiro began visiting and taking care of her brother. She chose as not to reveal her gender identity to him, especially given his proclivity for siscon. The only people in the dark about her gender are Itsuki and his close friends. She lives her life as a girl at all other times.

Chihiro, despite hiding her gender from her stepbrother, seems to have it her life in order. She knows who she is and isn’t confused or questioning about her gender. Chihiro just hasn’t challenged Itsuki’s preconceived notion. We do hope she mans up, pun intended, and just makes Itsuki face reality.

Ashley is one of those characters we don’t see nearly enough. She is a very eccentric 32-year-old tax accountant who takes over the financial lives of Itsuki and Haruto. She prefers to wear lolita styled dresses which makes her stand out and look even younger. She is an amazing accountant but has a sadistic streak. She loves to tease the boy, and by tease you could fairly say sexually harass. She has a clever way of getting her clients to reveal their fetishes through the use of their receipts for deductions.

In spite of her sadism, Ashley seems to have her act together. Ashley does run a successful business -- out of her home, of course, for the deductions. She accepts who she is and uses her skills to her and her client’s advantages despite embarrassing the hell out of them. The lolita accountant does manage to lower her clients’ tax burdens significantly. Her biggest flaw is that though her office may be neat and tidy, the living portion of her home is a disaster. She hires Chihiro to clean her home and finds out that she is indeed a girl but really pays it no mind. The people that are most comfortable with themselves are often the most accepting of other people’s life choices.

Haruto is one of Itsuki’s closest friends. He is also a fellow novelist and has even had his novels turned into an anime. Haruto’s career, despite debuting at the same time as Itsuki, is moving at a faster pace, outselling his friend. He has his own quirks, as all writers do; his hang-ups happen to involve maids. He has a younger sister who is a bit of a tsundere and can’t understand Itsuki’s fascination with little sisters.

He seems to have it all together, at least when you are looking in from the outside. He often posts to social media as a way to cultivate an image of coolness as part of his brand. The reality is very different. He is an otaku through and through. The shelves of his home are filled with figures and eroge video games. Despite the success of his books being made into an anime, the anime was widely considered to be a flop. The director used it as a place to give newcomers experience and wasn’t given the time or budget to succeed. He also developed a crush on Miyako, who is in love with his best friend Istuki. Especially in this situation, we see appearances can be deceiving and even the cool can be a disaster underneath.

Nayuta, which is her pen name, is the star of her publishing company. Her novels are considered genius. She is the youngest of the adults in the story at age 18. She had a rough childhood and was bullied and teased at school. She became an avid reader and fell in love with Itsuki’s novels and him in turn. She tried her hand at writing and won a newcomer award her career taking off from there. She has a few quirks like she’s only able to be truly creative when she is naked, so she does all her writing in the nude.

On the outside, Nayuta seems to have her life together, but we do see a few hints that it isn’t. The first and most glaring hint is that she hasn’t revealed her real name to any of her friends. Like many authors, she’s prone to writer’s block, yet, she finds the only way she can write is naked. Nayuta also lives in a hotel. She doesn’t live at home with her parents or in an apartment as a best-selling author can afford. Her profession of love to Itsuki seems to be sincere, yet she hasn’t come clean on what could actually be driving her devotion. She is proof that even though someone may seem to have it all they might not be as together as you think.

Itsuki is the protagonist of A Sister’s All You Need. He is a semi-successful writer with a contract for his light novel series about a magical school and the adventures of a brother and sister. Itsuki’s sister-centered series has more than 20 volumes published in the last 5 years. He is a pro at writing. He is an unabashed siscon, even though he doesn’t have a sister to dote upon (or so he thinks). Itsuki’s narrow field of view could be responsible for his limited success, but he has a loyal following. He is a writer and is prone to a lot of writer problems from writer’s block, to procrastination, to fighting with editors over ideas. He spends a good deal of his time traveling on “research” and hanging out with his friends, some of which are fellow writers. Itsuki also has two female friends that both have feelings for him. Miyako, who plays the role of the friend and has an unspoken crush, and Nayuta who is actively trying to convince him to marry her.

He may be living his dream as a novelist and open about his siscon fetish but he may not quite have his life together. Itsuki is constantly working up to his deadlines. He hasn’t realized that Miyako has a crush on him, and has turned down or won’t take Nayuta seriously. Itsuki hasn’t even realized that his little brother is actually his little sister. The end of the series has his life looking up but he really needs to get it together if he is going to find his way to the top.