[[caption-width-right:324:Sister Complex x 4.]]

''[[OniichanToIssho Onii-chan to Issho]]'' (official English title: ''[[OniichanToIssho Me & My Brothers]]'') revolves around Miyashita [[CherryBlossomGirl Sakura]], a second year middle schooler whose grandmother, who she lived with, recently passed away. Sakura then spent her days alone in her grandmother's big house until one day, she came home to find four strange men she has never met before living there! They explain to Sakura that until she was three years old she had lived with them, along with their mother and father.

There's the oldest brother Masashi, a romance novelist who [[WholesomeCrossdresser crossdresses]] when he isn't writing. The second brother is Takashi, who becomes a teacher at Sakura's junior high. The third brother is the [[FieryRedhead brash]] Tsuyoshi, a high school graduate and ''full-time part-timer" with a dream of owning his own shop. The fourth and youngest brother is Takeshi, a current high school student.

At first Sakura finds their presence to be intrusive, and is especially alarmed when she accidentally learns that she and her brothers are [[NotBloodSiblings not blood related]]. Eventually, she grows to appreciate their dedication to her as a little sister and values all of their moments together as a family.

As time goes on, Sakura graduates junior high and enters highs school. She finds herself becoming even closer to one of her brothers ... and not as a sister.

Written and illustrated by Tokeino Hari.
!!''[[OniichanToIssho Onii-chan to Issho]]'' provides examples of:

* AnimeHair -- Mizusawa, the DarkSkinnedBlonde (below). Also Tanaka, Rin, Masashi, and Sakura during the [[FestivalEpisode fireworks festival]] with their GirlishPigtails (below).
* ArrangedMarriage -- The family's ObaSan Michiyo, who raised Masashi after [[ParentalAbandonment the death of their parents]], arranged an ''omiai'' for Masashi for her husband's business associate's daughter. [[spoiler: However, Masashi informed Michiyo he would turn the daughter down for Sakura]].
* AuthorAvatar -- Portrays herself as a wind-up clock in the side columns in the manga.
* BigFancyHouse -- [[{{Ojou}} Kouzuki]] [[IllGirl Masumi]]'s father's mansion.
* BishieSparkle -- Happens very often around the brothers, and occasionally other characters, male and female.
* {{Bishonen}} -- Masashi, Takashi.
* BitingTheHandkerchief -- Rin when Tsuyoshi once rebutted her advances, and Masashi in reaction towards Sakura's coldness.
* BlushSticker -- Consistently used throughout the series by virtually ''everyone'', even more so than the also often used LuminescentBlush (below).
* ButNotTooForeign -- Rin inherited her blonde hair and blue eyes from her Swiss father. Her mother is Japanese.
* ButtMonkey -- Suzuki against Sakura's overprotective brothers, which is always PlayedForLaughs.
* CannotSpitItOut -- Sakura's first attempt at confessing to Masashi. Masashi, on the other hand, does not want to admit his mutual feelings to himself.
* CoolBigSis -- Masashi tries to have Sakura identify with him as a big sister and calling himself such by wearing fashionable women's clothing, doing his hair, and taking Sakura clothes shopping. This is all so that he could distance himself from Sakura's growing affections towards him.
* CherryBlossoms -- Seen throughout the series. Also seen right after [[spoiler: Sakura's and Masashi's FirstKiss]].
* CryCute -- Sakura manages this many times.
* CulturalTranslation -- Footnotes are provided regarding Japanese culture and terms in the manga.
* DarkSkinnedBlonde -- Mizusawa. See AnimeHair above.
* {{Delinquents}} -- Katagiri was close to becoming this, until [[spoiler: Sakura talked sense of responsibility into him]].
* {{Dojikko}} -- Sonomura.
* {{Doppelganger}} -- Murakami Michi, a women's magazine employee interviewing Masashi - who looks like [[MissingMom Sakura's deceased mother Fumiko]] - informs him that, afer meeting Sakura, she is not interested in men and delightedly says that Sakura is "just her type." She fawns over Sakura whenever she has an opportunity.
* DudeLooksLikeALady -- Masashi usually doesn't have to try too hard to look feminine. Even when he's not being a WholesomeCrossdresser he can take advantage of his face and long hair to look either very feminine or very masculine. Also Rin, with GirlishPigtails, feminine face and clothes.
* EvenTheGuysWantHim -- Mizusawa falls for a [[WholesomeCrossdresser crossdressing Masashi]] [[MistressAndServantBoy and calls him "Boss Lady"]]. This does not desist even when Masashi is dressed in masculine clothing. In general, most men who do not realize Masashi's true gender are attracted to him. Additionally, from Tsuyoshi's point of view, this trope also applies to Rin, his UnluckyChildhoodFriend.
* HairDecorations -- Sakura does not do this often since she sports a short bob, but when she does, it works. Masashi cannot help but do this as well.
* FaceOfAThug -- Coach Matsubara. Mistaking Masashi as a woman, he proposed to him. [[spoiler: Matsubara is a widower and wanted to find a new mother for his young daughter Haruko]]. Tsuyoshi can also be considered for this trope as he often gets annoyed with Masashi's antics. Oosaki-sensei fits this trope as well.
* FestivalEpisode -- There are two. Sakura and her brothers first went to a traditional Japanese festival, where Sakura ended up being a temporary PeggySue (except she keeps her current age) with a fourteen-year-old Masashi. The second festival is the fireworks festival that she and Masashi attended.
* FieryRedhead -- Tsuyoshi as a male example.
* FillerVillain -- Asada Tomoaki, self-proclaimed rival novelist to Masashi. He kidnaps Sakura in order to neutralize any energy she had been giving Masashi towards his writing and take some for himself.
* FirstKiss -- [[spoiler: After suffering amnesia and [[ImportantHaircut cutting his hair short]], Masashi seeks out Sakura at the park, cups her head in his hands, tells her she is not his sister, and they kiss - all in the second-last chapter of the series.]]
* FlowerMotifs -- Seen often on the manga covers, drama CD cover, and as backgrounds in the manga. Sakura and her brothers wear daisies in their hair on the cover of Volume 1. CherryBlossoms are often seen as well.
* {{Foreshadowing}} -- [[spoiler: Not long after Taizo tells Sakura she looks like his ex-girlfriend, who he lost long ago, she and her brothers find out [[LukeIAmYourFather he is her long-lost biological father]]]].
** [[spoiler: Masashi and Sakura's inevitable RelationshipUpgrade is about as subtle as a sledgehammer to the face. Anyone with even a rudimentary knowledge of shoujo cliches/tropes can see it coming from a mile away, what with ''every friggin' chapter'' making a point to remind the reader that they [[NotBloodSiblings aren't ''actually'' blood-related]], a chapter in the very first volume dedicated to Masashi's lost love for Sakura's mother (whom Sakura resembles mightily), that same chapter explaining that the then-three-years-old Sakura declared she would marry Masashi--a dead giveaway--and many more tip-offs.]]
* GenderBlenderName -- Nana.
* GirlishPigtails -- Tanaka, Rin, Masashi (very often; normally his hair is done up in a single ponytail). Sakura had very short pigtails with [[HairDecorations hair pins]] during the [[FestivalEpisode fireworks festival]]. See AnimeHair above.
* HalfIdenticalTwins -- [[ThemeTwinNaming Nana is the brother and Nene is the sister]]. While Nana's hair is short and Nene's long (Nana calls her "[[{{Samurai}} samurai]] hair") , they have identical faces. Nana used this to his advantage once by wearing a wig, disguising himself as Nene to fool Sakura.
* HintDropping -- Sakura does this a lot towards Masashi, as she is still working out her own feelings.
* IllGirl -- [[{{Ojou}} Masumi]], whose OverProtectiveDad worries about her [[IllGirl weak constitution]] and forbids her from leaving their [[BigFancyHouse mansion]]. She has a [[ShoutOut butler named Alfred]]. She likes Takashi.
* ImportantHaircut -- [[spoiler: Masashi does this just before seeking Sakura out and having their FirstKiss, listed above]].
* IndirectKiss -- Sakura worries over this when trying Katagiri's cooking with the spoon he was using to eat with. This also happens with Masashi at the [[FestivalEpisode fireworks festival]] when he offered her his bitten candied apple.
* LittleMissSnarker -- Tanaka, often towards Suzuki, when she's not being the PluckyComicRelief.
* LoveBubbles
* LukeIAmYourFather -- Sakura learns her biological father is [[spoiler: Fukasawa Taizo, the coffee shop owner / barista she befriends]]. This is [[{{Foreshadowing}} foreshadowed]] when [[spoiler: Taizo tells Sakura she looks like an ex-girlfriend whom he loved deeply]]. See ParentalAbandonment below.
* LuminescentBlush -- A constant in this series, done by almost everyone. Even more prevalent is the BlushSticker (above).
* MayDecemberRomance -- [[spoiler: Masashi is eleven years older than Sakura.]]
* MeaningfulName -- [[CherryBlossomGirl Sakura]], whose name was decided on by her brothers, stepfather, and mother while viewing CherryBlossoms, before she was born.
* {{Meganekko}} -- Sonomura.
* MiniatureSeniorCitizens -- Sakura's grandmother and Setsuko.
* MistressAndServantBoy -- Mizusawa is the one who enthusiastically fawns over "Boss Lady" Masashi, who is not amused with this. See EvenTheGuysWantHim above.
* [[NoblewomansLaugh Noblewoman's Laugh]] -- Masashi.
* NotBloodSiblings -- The manga takes great pains to remind the reader ''nearly every chapter'' that the heroine is in fact ''not'' blood-related to the titular brothers, despite the also-incessant reminders that they are all family and that Sakura is their "little sister." This is used quite blatantly so Sakura can be obsessively fawned over by her new guardiansóand eventually fall in love with one of themówithout the squick.
* ObaSan -- Michiyo, who raised Masashi after [[ParentalAbandonment his family's parents died]].
* {{Ojou}} -- Masumi, who has a [[IllGirl weak constitution]]. She considers "Takashi-sama" to be her prince. See IllGirl above.
* OlderThanTheyLook -- Takeshi is often mistaken as the oldest brother due to his goatee and quiet demeanor.
* ParentalAbandonment -- When Sakura was three, her mother and stepfather died. Years later when she lives with her brothers again, [[LukeIAmYourFather she finds out her biological father is]] [[spoiler: Fukasawa Taizo, who runs his own coffee shop. He left Sakura's mother Fumiko in order to become the "ultimate barista," and always missed her. He first tells Sakura not to think of him as her father and left for Italy, but returns when he changes his mind and is now a part of her life.]]
* PluckyComicRelief -- Tanaka, Rin, Masashi.
* PromotionToParent -- Mainly Masashi and Takashi towards Sakura. Masashi admits this more than anyone else.
* {{Samurai}} -- Nana sometimes calls his [[HalfIdenticalTwins twin sister]] [[ThemeTwinNaming Nene]] "samurai hair," likely due to her wide bangs off her forehead and long straight hair. Tsuyoshi also dresses as one during Sakura's field trip to Kyoto.
* TheShinsengumi -- Sakura and Katagiri dress as 16th to 19th century police in a movie theme park during their class field trip to Kyoto. Other regular characters dress as other people from the same time period at the park.
* {{Shojo}}
* {{Sidekick}} -- Suzuki and Tanaka, for Sakura.
* SliceOfLife
* StalkerWithACrush -- Sonomura towards Katagiri, who she likes and looks up to since junior high. Nothing over the top, she was just too shy to talk to him.
* TallDarkAndHandsome -- Taizo, Takashi, Takeshi.
* TemporaryLoveInterest -- Katagiri, who confesses to Sakura before he [[spoiler: moves away]]. He is grateful to Sakura for [[spoiler: talking him down for his [[{{Delinquents}} delinquent behaviour]] in the past, while his parents were getting divorced]].
* ThemeTwinNaming -- Nana and Nene.
* TokenMiniMoe -- Sakura.
* {{Transsexual}} -- Rin. While having a male body, she identifies herself as a girl.
* UnluckyChildhoodFriend -- Rin, towards Tsuyoshi.
* WholesomeCrossdresser -- Masashi, and averted for Rin. Masashi feels that, as a romance novelist, if he dresses and acts femininely he can better understand the female mind and use this in his writing. Rin, who is {{transsexual}} - as she admits she is a woman at heart - is the UnluckyChildhoodFriend of Tsuyoshi, whom she likes.
* WingdingEyes -- Masashi is the most guilty of this. [[ObaSan Michiyo]] also does this when once reminiscing about Masashi growing up, with stars in her eyes. [[MiniatureSeniorCitizens Setsuko]] does this when she first sees Tsuyoshi and mistakes him for a younger version of her deceased husband.
* {{Yakuza}} -- Hearing that Sakura is the temporary manager of the boys' soccer team, the over-protective brothers arrive at her school dressed in various [[{{Yakuza}} yakuza]] styles. Masashi, of course, [[WholesomeCrossdresser dresses as a female leader in an elaborate kimono]]. Mizusawa, mistaking Masashi as a woman, [[EvenTheGuysWantHim develops a crush on him]] [[MistressAndServantBoy and calls him "Boss Lady"]], much to Masashi's chagrine.
* ZettaiRyouiki -- Masashi rules this trope with [[WholesomeCrossdresser his various feminine outfits]].