I kinda forget who is who.
After a reread, i realize Iyu is only in the first 2 chapter, That why the girl that run to MC cry when she awaken and survive have different color hair. Yeah, she is another girl MC met since chapter 3 during the previous battle.
Which make me wonder, why even create the new girl Yotsuba in the first place ? you could combine them to just one character, just bring Iyu to that mission too, and fill that same role ? unless this gonna turn into a harem so you need to create more girl that just give all flag to just one girl
this lead to the possibility of Reika redeem pretty high and joint the harem. why create the chapter 5, showing the old Reika truly love MC. showing that, the shitty Reika is once different and was worth it. Since, if you want to just a shitty Ex, with some change in personally and not be shitty, everything is already good.