If you're looking for anime similar to A Sister's All You Need, you might like these titles.
Masamune Izumi is a high school student who writes light novels. Sagiri Izumi is a shut-in who never leaves her room. A year ago, she became Masamune’s little sister. But one day, Masamune discovers a shocking twist—The artist "Eromanga Sensei," who has been drawing illustrations for his novels, is none other than his little sister Sagiri! His cute little shut-in of a sister, who has been living under his roof, is using an obscene pen name and draws lewd illustrations?!
The premisis is pretty much the same where the MC has a little sister complex, their also a writer so if you like one then it's a safe bet you'll enjoy the other
Eromanga sensei is about how the parents got separated for some unforeseen event and remarried, and the mc ended up getting a shy little sister both of which are not related by blood. And they both work in the eroge/romance industry of writing. These two just have so much in common I mean look at the tags if you're not convinced lol.
Both series feature the MC as an eroge romance novelist who also has a little sister complex. Both MCs develop somewhat of a romantic relationship with their little sisters (who are not related by blood), and also develop good working relationships with their collegues in their industry. They also have the typical run-ins with their publishers.
Kyousuke Kosaka is a normal teenager with average grades and an average home life, but when he finds out that his overachieving younger sister Kirino has been hiding her vast anime and eroge collection from their unassuming parents, his world turns inside out! Now, having promised to help his formerly distant sibling navigate her two distinct lives, Kyousuke finds himself drawn into Kirino's world of magical girl anime and "little sister" fetish games while covering for his sibling to her parents and friends, not to mention trying to provide what guidance he can.
Rumors tell of a Stony Cat statue that grants a special wish: it will take one of your disliked personality traits and give it to someone in need. Two students arrive at the Stony Cat eager to make a change – Youto, an unabashed pervert, wishes to remove his façade and be able to speak his true feelings, while Tsukiko desires to hide her expressions and be more like an adult. However, little did the pair know that their prayers would be answered in unexpected ways – Youto begins to speak the full, embarrassing truth with brutal honesty, and Tsukiko becomes visually stoic, unable to smile, laugh or cry! To make matters worse, Youto soon runs afoul of the beautiful school idol Azusa, the girl who inherited his unwanted façade. Together, the three slowly become friends while Youto and Tsukiko try to regain what they've lost.
Shougo Mikadono’s deceased father left his son with a final request: attend his old high school to search for a suitable spouse, get married, and take his place as the rightful president of the prestigious Mikadono Corporation. Eagerly accepting the criteria, the teenager enrolls and quickly garners the attention of class rep beauty Konoe and one wealthy maiden after another due to his illustrious family legacy. What's more, Shougo then receives a very unexpected phone call from an unknown fellow student claiming to be his long lost sister - and she, too, wants to marry him! Can Shougo restrain his youthful desires while lustful beauties throw themselves at him in school, at home and even in his own bed long enough to determine who among them is his hidden little sister?
Yuu Nagami, a high school student aiming to become a light novel author has a little sister named Suzuka. Suzuka is an excellent student with good grades and great looks, but she's very cold toward her older brother. Every year Yuu keeps failing at the preliminary rounds of the light novel contest, but one day Suzuka reveals a shocking truth. The flirty sibling romantic comedy that Suzuka wrote has won the light novel contest! To make matters worse, Suzuka doesn't understand anything about light novels or moe so she begs Yuu to stand in for her under her pen-name, Towano Chikai!