Yohaji ships vs. IKEA furniture
Harumiki: Haru could understand the manual perfectly, and Miki is (as an oni) incredibly strong. They should be the perfect team. But☝ Haru is a loser and Miki has anger issues. So what really happens is: Haru knows they are supposed to use screw B now, except he dropped screw B 0.2 seconds after opening the package. Miki is about to take a baseball bat to their new shelf.
Izubara: Hatanaka tries to show off, saying "it's very straightforward, I don't even need the instruction manual". And he fucks up. Big time. Ibara (who still thinks he's the coolest person ever) sits down to help him and together they succeed. Of course, they have some trouble caused by the 4 children in their house, but it all works out in the end.
Gakutai (Ranmaru x Douman, not sure of the shipname): a snowball's chance in hell. Absolutely impossible. They are the one (1) ship I absolutely can not see even being in a situation where they would be faced with IKEA furniture, but if they were, they would fail. Epicly. Like, sitting around the eldritch abomination of a table they just created, getting drunk off cheap beer. (Both of them would have better chances working alone.)
Takayama: They can do it. Akira is used to working with 2D diagrams of 3D things (because of medical textbooks) and Makoto is great at following orders. Together, they are basically the perfect team for this (especially considering Akira's oni strenght). That is, of course if neither of them get called into work halfway through, and Akira doesn't start wondering what would happen if they did it differently (cue eldritch abomination).
Seidou (Seimei x Douman, not sure of the ship name): (Let's assume Heian era Japan had access to an IKEA.) Seimei decides that sitting back and watching Douman get progressively more pissed off is more fun than owning a new bookshelf (plus he already knows that they are bound to fail). Meanwhile Douman is cursing every person ever involved with the manual, IKEA or Sweden in general.
Feel free to add any other ships you want.
