"Masturbation is nothing to be ashamed of. Sometimes, while thinking of Onii-sama, even I...♡"
"Onii-sama's stiff 'thing', it's been poking me in the back for a while now."
"If it's Onii-sama, I would gladly allow you. No, it has to be Onii-sama! If it's you, then it's okay to mess up and break my body."
"Onii-sama's scent, breath, voice and down to your single last cell; I find them so endearing and loveable that I can't hold back any longer."
"I'm full just by breathing in the same air as Onii-sama. Why, I'm so full that I feel like I'm pregnant with Onii-sama's child!"
Oh yes, it's THAT kind of
If you have any issues with ecchi or incestual themes you should probably stay a long way away from this as there's plethora of that in here. SekaImo is probably the most perverted light novel I've ever read. What's interesting though is that it is not really lewd in a "physical" way. There isn't much in the way of boob groping or panty shots or stuff like that, but rather the dialogue itself is pretty much borderline hentai more often than not. The quotes above are just some examples but really there are countless more lines like that spoken in just the first few chapters of the story.
What story you may ask? Well it's a typical self-insert Korean high school protagonist named Siyoung, who one day gets kidnapped to Romania by a heterochromatic rich girl who claims to be his little sister. She is known as the "Princess of Pure Darkness", the leader of a multinational military company that feeds off of other people's anguish and misery. Despite her malicious nature however, towards her brother she's a completely different person and she loves him with all her heart.
And when I say she loves him, I mean she really... really loves him. The novel's title means "The World's Greatest Little Sister" and of course it refers to the girl herself: Maria Lunalady Blackhazel. She is without a doubt one of the absolute horniest characters and most extreme brocons I have seen in a long, long time. She doesn't even try to hide her feelings in any way, she pretty much publically announces that she wants her brother to have sex with her, do all kinds of lewd things to her and eventually marry her. She's every imouto-fetishist's wet dream, and pretty much feels like a character written solely for the purpose of giving the middle finger to all those people hating on incest in this day and age.
Then there's also her younger twin sister Dorothy, who is very similar in personality but has a different target for her affections. In the same way Maria is head over heels for Siyoung, Dorothy is hopelessly infatuated with Maria herself. As a consequence of that she also hates Siyoung's guts and more or less wants him to go die already since he's taking all of Maria's focus and attention for himself, albeit unwillingly. The weird love triangle in-between the three of them reminds me a lot of the relationship between Mahiro, Nyaruko and Cthuko from Haiyore! Nyaruko-san, in case you've seen that.
Now I'm sure this all sounds like nothing more than non-stop blatant fanservice, but here's the real surprising part: despite all that SekaImo actually has some darker elements to it. Like I mentioned before, Maria is the leader of the Blackhazels and their ruthless military organization, and she's not afraid to show it. She actually possesses some serious Yandere characteristics as she would rather murder a hundred innocent people in cold blood with her own two hands than see her brother get the tiniest injury. And that's not just metaphorically; I mean she'd really do it. You know those cruel torture scenes in for example Higurashi or Kaiji? Maria does those kinds of things as well, and does not hesitate to kill anyone that happens to stand in her way. And seeing as the Blackhazel family has many enemies both on the inside and the outside that seeks to harm them, there is no shortage of people doing just that.
So there are basically two polar opposite sides to this story. Most of the time it provides borderline hentai incest fanservice, but sometimes it also involves murders and gruesome torture. Not a combination you see every day.
At the time of writing this only the first volume has yet been translated (the second one is currently work in progress) but I still think it gives a pretty clear image of what kind of story SekaImo really is. I would recommend this to anyone who a) likes fanservice and incest, and b) appreciates sudden 180 degree flips as far as atmosphere goes. It's both extremist and unorthodox at the same time in that sense.