When their parents passed away, Akiko and Akito Himenokouji were separated and sent to live with different foster families. Now 6 years later, they are finally reunited and are not only attending the same high school but are also living together, a win for Akiko. You see, Akiko loves Akito very, very, very much, and although he doesn't feel the same way about his dear sister, she's determined to capture his heart. Of course, things start to get harder for her when several other cute girls from school move into the sibling's love nest, all eyeing up Akito for themselves. Will her sisterly love be enough to sway him in the end?

Oniichan dakedo Ai Sae Areba Kankeinai yo ne and Kono Naka ni Hitori, Imouto ga Iru are both very fun and light-hearted series, with the main themes being cute girls, comedy, and fanservice (lots and lots of fanservice). Of course, that's not forgetting the key element, the little sister! In NakaImo the sister character is a surprise for us all but we know she's in there somewhere, whereas in OniAi we're very much aware of who the sister character is. Both situations are pretty great for their own reasons, but the important thing is that the sister is there.

As mentioned before, both series have their good share of other girls as well, and although the archetypes used in both shows are fairly different, if you liked the girls of NakaImo you'll surely love the cuties in OniAi as well. So if you want something light and funny to watch with added little sister, be sure to check out Oniichan dakedo Ai Sae Areba Kankeinai yo ne!

If you know anything about visual novels or even harem shows, you've probably heard of flags: events or indicators that change how the story continues. So what if you could see those flags in real life? Does the girl like you, is she angry, is she going to die? Souta Hatate is fortunate enough to have such an ability, though half the time it causes him hassle more than anything. Now living in a school dorm with a myriad of cute girls, his flag vision ability is working overtime to keep up with all the events that are popping up, which is concerning considering the number of death flags he's been seeing recently.

Another light-hearted school based series for the list, Kanojo ga Flag wo Oraretara focuses mainly on cute girls and it's flag vision device for a majority of the series, which is actually very entertaining, as exaggerated tropes often are. Along with the series having a similar overall setup and atmosphere to NakaImo, there is also an ever-present feeling like there's something being hidden from the protagonist, as well as the viewer, which keeps the series interesting as more and more gets revealed. In NakaImo this is obviously the question of "who is the imouto?", whereas in Kanojo ga Flag wo Oraretara, we, unfortunately, can't say much without revealing the plot, but we're sure you'll be surprised!

Originally living an ordinary life as a high schooler, after an accident takes the lives of his parents Teppei Arima is taken in by his grandfather, a businessman of great wealth and influence. Now the heir to the Arima Financial Combine, his daily life has changed from kendo practice and school commutes to high-class balls and school commutes...in a limo. On top of all this, he's now attending Japan's most prestigious high school, which is proving a bit too much for an ordinary guy with no knowledge of high-class etiquette. Fortunately, he has his own personal maid, a princess, a beautiful fiancee and a fiery tsundere to help him figure things out.

Both Princess Lover and Kono Naka ni Hitori, Imouto ga Iru feature protagonists that have come into a lot of money, or rather, have entered the world of the elite by chance. Of course, this setting also includes a number of cute girls hoping to get much, much closer to our protagonist, and who often get themselves into ecchi situations. In fact, the fanservice and ecchi are consistent in both series, with Princess Lover demonstrating a mastery of camera angles to ensure the highest number of panty shots possible. Although one of the older series on this list, Princess Lover has aged surprisingly well and we'd certainly recommend it to any harem fans.

Kyousuke Kousaka and his sister Kirino do not have a good relationship. While he is an average high schooler in most respects, she is a top student and model, a typical popular girl, and sadly these two personality types tend to clash under the same roof. One day, however, Kyousuke accidentally finds one of his little sister’s eroge games, something which she at all costs wants no one else to know about. Agreeing to keep her secret safe, she drags him into the world of anime and otakus, and their still precarious bond begins to get more complicated.

The key similarity between Ore no Imouto ga Konnani Kawaii Wake ga Nai and Kono Naka ni Hitori, Imouto ga Iru is, of course, the little sister element. While both end up with a full harem situation on their hands, the focus of both protagonists is their little sister, despite the number of other beautiful girls surrounding them. In both situations what starts off as simple brotherly love turns into something more interesting and perhaps morally questionable later on, but then that's what we're all here for isn't it?

Beyond that, both series start off fun and ridiculous but do take a slightly more serious route down the road so you can look forward to a decent plot. As OreImo also has a second season which brings the show to an end, we'd recommend it to anyone feeling dissatisfied with series like NakaImo often lacking a true conclusion, which we rarely get with these kinds of shows. If you like little sisters, Ore no Imouto ga Konnani Kawaii Wake ga Nai is the iconic series you need to watch!

Raku Ichijou is just a normal highschool boy who's in love with a normal highschool girl, though of course he daren't confess his feelings. That said, he's also the heir of a yakuza family. So when a renowned gangster family moves into town, things start getting messy, that is until Raku's father and the new gang's leader find a way to stop their henchmen fighting: Raku will date the gangster's daughter Chitoge Kirisaki to form a truce. Raku and Chitoge's personalities couldn't be more different, however, and they certainly have no desire to date each other.

For the sake of their families though, the two will try to keep up their fake love, but with Raku still crushing on his classmate, and a promise he made to a girl 10 years ago always in the back of his mind, things are not so simple.

Like NakaImo, Nisekoi has a large focus on the characters' past and how they're connected to each other, while the present story is ongoing. As more about the past is revealed and present relationships continue to progress, everyone's feelings for each other become more complicated and confusing. It's this back story to the characters that makes both series enjoyable to watch not just for the cute girls but for the story as well.

In addition to this, we have the rich characters setting, which although neither series focuses on overly, allows for more freedom in the story and locations due to the abundance of money everyone has. If you're into harem series like Kono Naka ni Hitori, Imouto ga Iru you've likely already heard of Nisekoi, but if you haven't had the chance to watch it yet, now is the time.

Keita Suminoe is in a for a surprise when his father gets remarried and he gains a couple of cute sisters in the process. The twins Ako and Riko are actually very pleased with the new little brother they've acquired, in fact, if anything the fact that he's their brother seems to be a turn on for them. Keita, on the other hand, may like his new sisters, but he has no intention of dating them, much less doing the lewd things that they're interested in. But this is a two on one battle, and one which he appears to be losing quite badly, though who can blame him when he's up against such pretty, ecchi step-sisters.

Here's another sister filled series, but this time there are no imouto's, only onee-chan's, though they're both still cute as heck. Although the sisters here are not a secret like in NakaImo, the most important thing about the girls in both series is how aggressive they are with their advances, as none of them have any intention of letting their boy run away or worse, get with another girl. So as you can imagine, if you liked the fanservice and ecchi in Kono Naka ni Hitori, Imouto ga Iru, you'll love the abundance of it in Kiss X Sis, with the series being borderline hentai in half of the fanservice scenes.

Kiss X Sis actually has two adaptations: the TV series and the OVA series which we've recommended here. The OVA series has a lot more ecchi so we'd suggest checking that one out first, but if you happen to enjoy it definitely check out the TV series as well!