This is my Valentine's art submission, starring Leona Garstein and Tasuku Shinguji from the Super Robot Wars series of games and animated series.
The best jokes need no explanation, but this isn't one of the best jokes. I will caveat that and say that in some cases, even good jokes need explanation if you are unfamiliar with the cultural background that they come from.
In this case, the background knowledge you need comes from playing Super Robot Taisen Original Generations 1 and 2. I'll explain it for everyone else:
Okay, so you've got a game, and in the game Tasuku and Leona are slowly becoming a couple. Tasuku is a goofy sort of character and likes jokes and whatnot, Leona is far more straightlaced.
Leona has a cousin named Elzam, and for a portion of the game he wore a disguise that really wasn't all that disguising, and called himself "Ratsel Feinschmecker", which translates as "The Mystery Gourmet". This was an appropriate name, as Elzam is a very good cook. The disguise he wore is the same costume as Leona is currently wearing. Everyone played along with it, I guess to not make Elzam feel dumb for picking such a cheesy and obvious costume.
Leona, on the other hand, is not a good cook. The only food she can make well is porridge.
So, let's put it all together- Leona is wearing the "Mystery Porridgemaker" "Disguise" and roleplaying with Tasuku, who being a goofy sort is happy to go along.
The line Leona uses is one of her battle cries, if you are wondering, and it's what inspired this pic in the first place.
I expect that Leona will never live it down if Katina catches them doing this, however.