I've long pointed to Elfen Lied as having the most explicit and polarizing opening scene of any anime series I've seen, but it may have found a worthy challenger in this light novel adaptation from the fall 2017 season. A Sister's All You Need's ridiculously trashy, over-the-top portrayal of a little sister fetish taken to the extreme is memorably jaw-dropping in its audacity. Although it is quickly revealed to have been a joke, as protagonist Itsuki lets his fetish run wild for a story proposal, its humor is extremely hit-or-miss and works better in retrospect. Fortunately, later renditions of Itsuki's off-the-wall little sister ideas are much funnier, and that's just one small gimmick of a story that otherwise focuses on adult writers and the people who regularly interact with them.

It's a potentially interesting approach, as while anime has numerous stories about manga and anime creators, stories which focus on light novel writing have been rare. In rare examples such as Eromanga Sensei or Saekano, the featured writer is still a high school student, so having the writers be actual adults (even if one is only 18) offers the potential for a slightly more mature angle. That doesn't prevent some of the series' humor from being juvenile, such as Nayuta's constant efforts to have Itsuki's “dick for dessert” (or something else along those lines). However, it does allow for some scenarios that only work with adult characters, such as one episode where Itsuki literally gets locked in a cell until he meets his deadline or an amazingly funny take on an accountant visiting to do Itsuki's taxes.

The show primarily follows the exploits of the central tight-knit group with a focus on various aspects of their writing trade, such as dealing with editors and writer's block, taking vacations thinly-veiled as research, maintaining an online persona, dealing with manga and anime adaptations of the writer's work, and so forth. While some of this is insightful, by far the most hard-hitting and poignant moment is Haruto's experience with the anime adaptation of his novel series. The series also has other moments where it stretches for more serious impact with its characters, such as Itsuki's frank admission to himself that Nayuta is a more talented writer, Haruto's envy that his work isn't as creative as Itsuki's (even though Haruto's more calculated writing is much more successful), and the harsh realizations that some characters come to about potential romantic entanglements.

The occasional gross tastelessness of some humor aside, the series struggles most in handling its more serious content. It's not so much an issue of individual scenes being handled poorly, as some of the series' strongest moments come from isolated moments, but rather how well they're timed and framed in terms of message. As a result of this, the three central writer characters usually come off in a negative light. Each is terribly self-centered in an unflattering way; Itsuki is highly egocentric in addition to his little sister fixation, Nayuta is perpetually wrapped up in her carnal desires, and the seemingly even-headed Haruto is consistently willing to sacrifice artistic integrity for success. It's possible this was intended as some combination of a classic ego-id-superego triangle, illustrating that writers tend to be a difficult lot in general, but the writing is hit-or-miss in how effectively it makes these characters sympathetic. Meanwhile, the more easily likable Miyako functions as the audience viewpoint character, the outsider looking in and occasionally getting caught up in shenanigans.

With not much of an overall plot structure, the series spends a lot of its time indulging in the whims of its original author, which makes me suspect that Itsuki is at least partly a self-insert for Yomi Hirasaka, who also created Haganai. (Some aspects of Itsuki's background definitely fit with what Yomi has previously admitted about himself as a student.) One regular feature is indulgence in exotic beers and other liquors, which are regularly featured in eyecatches and end cards. Another is various board and card games, a common source of humor in the series, though one game in the final episode seems more intended to be a harsh reflection of reality for writers. Many real-life popular board games can be seen in background shots of Itsuki's room too; I've played several of them myself. Fanservice is also a semi-regular feature, as Nayuta does her writing in the nude, Miyako is manipulated into stripping down on a couple occasions, and most of one episode revolves around whether characters in the manga adaptation of Itsuki's novel are better off portrayed naked or with attractive undergarments. You can also keep an eye out for allusions to numerous other anime titles from the past decade, including Oreimo and The Melancholy of Haruhi Suzumiya.

The production effort is not one of the sharper ones by SILVER LINK. Character designs are appreciable enough and some nice background detail can be seen in the portrayal of Itsuki's room, but too often the artistry looks rough and the gameplay scenes can come across as animation dodges. The musical score does a sufficient enough job to not be distracting but it rarely stands out either. The fanservice can get racy, and one of the funniest protracted scenes involves a character in a story wielding his giant penis as a weapon, but even with Nayuta's saucy language, this series is tame compared to a lot of ecchi fare these days.

So far, Funimation has done a solid job with its casting choices for the English dub. Amber Lee Connors is a delight in a limited role as accountant Ashley Ono, but most of the roles are appropriate in both casting and performance. The exception is one performance which makes a character's not-so-hidden secret obvious enough that the lack of other characters noticing strains credulity even further.

Overall, A Sister's All You Need is a decent series that shows flashes of being good, but it also has an annoying tendency to shoot itself in the foot with occasional awful scenes. Its ending is unfortunately not one of its better moments, as the whole last episode doesn't seem well-conceived, and the resolution that one character gets isn't enough to offset a total lack of closure on other key character threads, especially the matter concerning Chihiro. Still, if you can get by the barrier posed by its first scene, there is some entertainment value to be found here.