DISCLAIMER: All characters rights go to Konami and the Bemani franchise!
So I have been setting this prank up for about 3 weeks now, but unfortunately the fruits of my labor came to fruition yesterday. All for the best, I guess.
Background: Kanoko and I are very healthy and we eat the same thing for breakfast every day, well maybe a solid 350 days a year. It is egg whites and toast. It has got to the point that if I don't eat this for breakfast, my entire day feels "off." I put salsa on my eggs while she uses ketchup, and she HAS to have ketchup, or else she will not eat breakfast. We have a backup bottle or two in the pantry just in case she runs out.
About three weeks ago: I notice that her bottle is running pretty low and she has to actively shake the bottle to get the last bits out. We are pretty earth-conscious as well, so nothing goes to waste; use until the last drop! There is still just enough left in the bottle that I can tell Kanoko is thinking that she shouldn't recycle it just yet, and sure enough, she puts it back into the fridge. I notice this thought process going on in her head, and decide I should mess with her. Once we finish up breakfast she goes to get ready. I take one of the full bottles of ketchup and add just enough to the almost-empty bottle so that she will have the amount needed for breakfast the next day. Breakfast the next day rolls around, and she does the same thing: adds ketchup to her breakfast, decides there is just enough to save, and puts it back in the fridge. I again refill the bottle with just enough for the next day. I should also mention that Kanoko is short, so I hid the "refill" bottle at the top of the pantry so she couldn't see that it had been opened and used.
After a couple of days, slyly watching her add ketchup to her breakfast, I can begin to see an intrigued look on Kanoko's face while she is prepping her breakfast. She doesn't say anything, but you can tell she has taken notice of the bottle. This goes on for another seven days.
Week two comes along. Breakfast continues to go off without a hitch and, every time Kanoko adds the ketchup to her breakfast she gets a little twinkle in her eye: like she really, really wants to say something about it, but doesn't want me to make fun of her being crazy and thinking the ketchup bottle is "never-ending". It gets to the point that she will look at me, start to say something and then stop herself, change the subject, and put the bottle away. I have never looked forward to breakfast so much in my entire life.
Week three: Kanoko is on the verge of saying something everyday. It's becoming hard to not laugh while watching her add the ketchup to her eggs, but GOD am I laughing hysterically on the inside. At this point I have used roughly a half-bottle of ketchup, just for the sake of refilling the other one.
Until finally, yesterday. Kanoko adds ketchup to her breakfast and looks me directly in the eye, and dead serious says:
"Roku, we have a magical ketchup bottle."
I could not control my laughter and proceed to lose it entirely while she tried to explain to me how she has used the exact same bottle of ketchup for 3 weeks and it has been almost "empty" the entire time. She now thinks I am laughing because of her belief in magic and she is trying as hard as possible to convince me that she is serious and it IS magic. So I proceed to go into the pantry, take out the half empty bottle of ketchup and place it on the counter. It all finally clicks in her head, and at that moment the empty ketchup bottle clicked into my head. It hurt like hell, but I don't care because I made a magic ketchup bottle happen, so I am essentially MZD.
TL;DR Made my girlfriend believe we had a magic ketchup bottle, but it hurt just as much as a normal bottle when flung at my face.