If you're looking for ideas, I've just posted a couple new ones in the ideas thread and there are always a ton of old ones sitting there waiting for someone to pick them up.

And here's a bonus one.

I originally envisioned it with Evangelion characters because of course I would, but it would probably make more sense with characters from the Fate series, now that I think of it... but anyway, the original idea was that Shinji is a member of archery club and on one day Asuka asks him to teach her archery. He says sure and asks his girlfriend Rei to be their targert just becsause she happened to be around. Rei casually obeys. The core of the story is Asuka shooting Rei with arrows under Shinji's close guidance and how everyone is casual about it. To elaborate, there's plenty of body contact as he guides her hands with his and presses himself to her from her back guiding her whole pose and such, and in my mind the characters themselves see it as casual and non-sexual (same goes for their attitude to using Rei as a target thus killing her). In the end they either leave Rei bleed out to death or finish her with an accurate shot to the heart for which Shinji praises Asuka saying she now mastered archery. Bonus point for Rei being pregnant with Shinji's child (that is, if you do pregnant guro). In this case Shinji might choose Rei not only because she happened to be around, but also because her pregnant belly looks like it would make a great target. Rei might even be being pregnant with twins (either boy and girl or both girls) and when Asuka ruins Rei's belly with arrows enough for the babies to be seen, they see the twins holding hands and smile at how cute it is, and then just casually continue the target practice, maybe even start aiming for the babies. Or the other option is after the target practice Shinji and Asuka come to dying or already dead Rei and upon seeing her ruined belly close see the twins holding hands and also find it cute (and Rei also finds it cute, if she's still alive), and then they casually walk away, leaving Rei and the babies to die, or take her body to the nearest dumpster first. Or they see the twins when they go to retrieve the arrows and add up Asuka's current score after having run out of their first batch.

Also before shooting might have a part where either Shinji, or Rei herself paint her belly, tits and pussy quickly with a paint brush to make targets, with belly button, nipples and clit being at each target's center respectively. Though where would they take the paint? Cause I was thinking of the whole thing to be kinda spontaneous, like they are on their way from school and Asuka says "hey, Shinji, by the way, can you teach me archery?" and he's like "sure, Rei, go stand there, you'll be our target". Cause if they do it in the archery club, there's no reason to use Rei as a target, the archery club should have targets. And if they are on their way from school, Shinji might have his bow and some arrows with him, but no one would have any paint with them. One solution is on the way home they're passing by an empty lot where people are painting a mural on a wall, so they either ask to borrow some paint if the people are still there, or just use it since it's there, if the people are gone. Another option is they just scribble the circles on Rei's body with an arrowhead, but paint would probably work better.

And as I mentioned the whole thing would probably make more sense using characters from the Fate series with Shirou teaching archery to Rin, I guess, and their target can be Sakura or maybe Illya. But somehow my imagination doesn't want to work that way, putting Eva characters in this story instead even if it makes little sense... hmm, wait a moment... somehow it have just occurred to me that Sakura was also a member of the archery club, apparently joining for the purpose of getting close to Shirou, so I wonder what effect that would make on this idea?.. Like, maybe instead of using Sakura as a target it is set at the time when Sakura have just joined and so she is the one in need of teaching? But then who would be the target? As I guess that would be far before the grail war and this introduction of most of the characters, there's only Rin, but at this point she's just another random girl from the same school (are they even in the same class?) And the whole point of the original idea was how even if Rei is Shinji's beloved girlfriend (maybe even pregnant with his children), he still sees nothing wrong in spending her life like that even though they could just return to the school with its archery range, but that would take time and Rei is handily right here, so let's use her instead... anyway, that wouldn't be quite the same if the protagonist didn't care for the target girl in the first place.

SPOILERS FOR PRISMA ILLYA
So, maybe, if going with Fate characters, it can be set in the universe of the Oath under Snow movie and Miyu would be used as a target. Though Miyu doesn't go to school. So either this happens in a yet parallel universe where the second half of the movie didn't happen and they just lived happily ever after and Miyu started attending school and then on one day Shirou, Miyu and Sakura walked home together and that's when Sakura asked if he can teach her archery. Or, maybe it can work even better, if instead Miyu still doesn't attend school, but Sakura visit's Shirou's home and that's when she gets the idea to join the archery club in the first place to become even closer to Shirou and so she asks him to teach her and they use Miyu as a target.
END OF SPOLERS

Or just screw it all and go with Eva characters just because. Anyway you're the author here, so see which works best for you, in case you're even interested anyway.