Both stories have a black haired protagonist (Shijima and Sorawo) who isn't aware of her attraction to the more obviously gay blonde woman (Majime and Toriko) that confesses her love to the protagonist frequently. Majime also has an egg as her identifying trait while Toriko has the kanji for bird in her name, which is pretty funny. Both couples had a really bad first time having sex, with Shijima and Majime having it a lot worse as Shimeji runs away in terror, where it was just really bad sex for Sorawo. However, when they combine again through surreal, extradimensional means, it's different how they end up.
Sorawo and Toriko end up fully becoming one unit. They are their own people, of course, but trying to discuss one without the other is pointless. There's no way to describe them, not partners, accomplices, lovers, wives, spouses, friends, nothing. No single stock character dynamic could perfectly fit them. They're just Sorawo and Toriko. In Shimeji Simulation, they give each other a little part of themselves, but never fully become one unit.
If you clicked this spoiler without reading Otherside Picnic, I'll recommend it again. It's more concrete than Shimeji Simulation, as it's set definitively in Japan and draws from early 2000's Japanese creepypastas for its horror. While I'm sure this may have you a bit doubtful, it's done incredibly well and is explained in a way that just engaged you even more. The entire series is, even more so than Shimeji Simulation, built around the relationship between Sorawo and Toriko, the two most important characters in the series. I hesitate to call them both main characters, because while Toriko is incredibly important, the only POV we ever see is Sorawo's, and she has a very strong narrative voice. The book is written in a way where there's not too much character in the narration that it obscures event, but enough that you can still easily tell Sorawo is the one narrating. You can read through, think about what Sorawo is describing vs. how it compares to her interpretation of it and tell "Huh. She is definitely biased on this." For example, Sorawo constantly thinks about Toriko and how attractive she is and how she must have so many friends. In reality, she's pretty antisocial and barely more social than Sorawo, but Sorawo is just constantly thinking "Oh she's so incredibly attractive she probably has a ton of friends and is super popular," so you never really notice. Also they don't talk to other people too much. I'm pretty sure there are only ten named characters that appear in multiple volumes.
TL;DR: Read Otherside Picnic, very good book series. Read light novels first, easily the best way of enjoying the story. Then manga, if you feel like it. Still pretty good. Then maybe the anime, but it reorders the first volume and a half to fit into a conventional 12 episode anime season, which really doesn't do well when there's eight volumes out and probably at least one more.
