It's been a while since I posted an idea, so here's one.
It came before the "Sunny Day" and in some parts is kinds the opposite.
One happens on a sunny day, another on a rainy day.
One has them go for the very first snuff method, another has them consider various methods.
One has actual snuff happening, another hasn't (though if you want to pick up the idea, feel free to add actual snuff into it if that's what you feel would fit better).
Anyway, here it goes...

Shelter from the rain

(Evangelion, Ayanami Rei, various snuff methods considered casually but not actually happening)

Shinji and Rei are on their way from school when suddenly a heavy rain starts. They take shelter in the nearest shop. Which appears to be a "snuff shop" or maybe a "snuff cafe", where you can have yourself snuffed. It is usually used by couples who find it incredibly romantic to be snuffed together or have on of them watch and/or help another being snuffed. The "cafe" doesn't imply cannibalism, but rather a romantic atmosphere of a couple sitting at the table, reading through the menu of different options of how to be snuffed and discussing what to choose, like they would choose food in a regular cafe. Maybe they’re also given some light food to eat along the discussion like a small cake and some tea. So Shinji and Rei take a seat at the table near the window and a waiter brngs them the menu which is probably the first time they realise what kind of a cafe this is. Or maybe Rei noticed it from the start but didn't consider to be significant enough to mention. Shinji is a bit embarrassed by suddenly getting in a romantic situation with Rei, while Rei pragmatically suggests to study the menu at least to kill time until the rain stops. Though if something from the menu would be to their liking, there's no reason not to go for it, is there? So the most part of the story is supposed to be Shinji and Rei reading about different methods to get snuffed (different methods may include snuffing one of them or both), but every time one suggests something, the other comes up with a reason not to do it. And the reason is not concern for their own or each other's life, but something like discarding death by drowning because Rei doesn’t have her swimsuit with her. And so they check the next option in the menu…
The story ends with Shinji and Rei noticing that the rain is over, so they casually continue their way home, deciding to come back some other time. Yeah, I know, such an ending means there won't be actual snuff in the story, but then again it would be a nice twist, and will emphasize the overall casual attitude.

> Anyway you could have shooting her but Shinji isn't confidant he can use guns…maybe using a sledgehammer but either one isn't sure they can lift it.

First Rei suggests the sledgehammer, but Shinji says he can’t lift it. Rei then looks at the option of being cut in halves (vertically or horizontally) with a chainsaw, but figures out Shinji won’t be able to handle it either. So she suggests shooting her with a gun, and while Shinji believes he can handle it, he’s sure his aiming will be totally off, so he can accidentally shoot her in her heart or even head and kill her before he could enjoy her suffering a lot.

> If it's for couples maybe the store could offer a dual stake burning but they decide not to as they wouldn't be able to enjoy the others agony….crusifiction would take too long so that could be ruled out.

> Pushing off a high ledge…but one or the other is afraid of heights. Torn apart by dogs but the store doesn't have any, eating a timed explosive but not sure if they could swallow it?

Well, if there are no dogs why would they be on the list? Let’s say the option is called “eaten alive by the dogs”, and another customer went for it a while ago, so the dogs are not hungry right now.

Hanging – is recommended to be done during sex because of how it intensifies it, but Shinji and Rei’s relationship isn’t that far yet.

Garrote – if Shinji uses a garrote on Rei it means he has to stand behind her (now that I think of it, it probably doesn't though), so he can’t see her face as he kills her.

Seppuku – is discarded because of it’s association with dishonor.

Gutting/Disembowlment - ???

Cutting to pieces - ???

Skinning - ???

Beheading - ???

Electrocution - ???

Cutting open Rei’s skull and destroying her brain – the brain doesn’t feel pain, so it would be boring

Crushing by a press – won’t allow Shinji to see the process

Acid bath - ???

Cutting Rei’s throat - ???

Impaling through the pussy to the mouth – Rei wants Shinji to be her first, not a pole

Meat grinder - ???

Poison - ???