^theres a good summary in chapter 4 comments. Chapter 1-5 is linear. 6 is the prequel of 5.
About the confusing characters, the easiest way to keep them tracked is on the chapter 4 comments I mentioned. So you'll get who's who.
Based on this chapter which is the prequel tnay left open ended for two where Makoto made her choice and where Mariko given one as well before getting seemingly the same drug by Saegusa. Do keep in mind, it's Saegusa that cause all this in the first place and probably the one who gave the drugs to other people. Not this dude in chapter 6 .
For sure the girls in this chapter were all still a man. In summary Makoto had a choice to either live with his wife again or be a slut with another man forever. The case of Mariko left ambiguous like Makoto and Saegusa case in chapter 5. Based on my impression it seems all of them made a choice of not returning to their body. Case like Karen and Kikyou in chapter 2 and 3 seemingly left behind as well with their partner never actually found who themselves was or what happened to the girls soul after they got swapped.
The case for Makoto/Saegusa, Yuuya/Mariko kind of explained but left ambiguously. Yuuya guy that got his wife pregnant body seems still on her body in this chapter. Unsure about chapter 5 but since She said "You'll have to make choice" means Yuuya decided to stay on bed wife body which the answer seemingly left to the husband side (the one who got their wife body) just like Makoto much later in chapter 5. In chapter 6, we see 4 of them seemingly still get their body swapped. For Saegusa case this was obviously the prequel before chapter 5 happened. The last page also abit ambiguous because the usage of they and "Makoto". Who would you congrats for giving birth? The mother or the father? Also I am sure he also realised that Saegusa throughout their fuck bud days doesn't felt like a Saegusa herself.