It's funny cause last night, Daulton (my BF) was telling me about this anime film called "Mezzo Forte", where it's a really nice anime movie until . . . they drop a hentai scene right squat in the middle of it. Like WHOA that was out of nowhere, wish I had gotten some kind of warning or foreshadowing to this happening.
^^^^ If that last statement is how a reader might feel about a certain scene, and not in a positive "WOW THIS IS REALLY HEATING UP" or "WOW THE TABLES HAVE REALLY BEEN TURNED" kinda way, then chances are, you proooobably should exclude it.
This basically hits the nail on the head:
If you want to just add a sex scene in there or something simply because you want to attract readers to the fanservice - don't do it. Most of the time, you end up doing your story more harm than good, and if it doesn't benefit from this sudden happening in any way shape or form, then that's all it is - fanservice, and in the end, fanservice only satisfies people for a short amount of time; it's the overall story you want to stick with them, and the fanservice doesn't need to be a part of that.
If your comic is cute and fun and adorable and using themes of friendship and love, it can be very, VERY difficult to pull off the sudden "OH NO NOW THEY'RE ALL GOING TO DIE IN A SEA OF FIRE". Some stories it's worked for, but that's only for a very, VERY set few, and they usually have some sort of foreshadowing or build-up leading to it. Don't slap boobs and sex scenes and nudity and swearing and violence in there just because you want to attract new readers. At that point, you're just selling yourself out, and is almost an insult to the readers who have been dedicating their time to actually following the story since day one.
I think one of the only shows/movies I've seen that has successfully pulled off the "SUDDEN DEATH AND EVERYTHING IN A HAPPY STORY" was Barefoot Genji, and that's because that story ended up being about the bombings of Hiroshima during WWII. It had that ground to be built on and was based on the author's own experiences as a bombing survivor, and wasn't just thrown in there because he wanted to appeal to the other spectrum of readers who read things only for fanservice and whatnot (first thing that comes to mind for me when I mention that? Highschool of the Dead. It's always just been fanservice-y to me and that's why it never appealed to me).