Thanks for the chapter!
My bet is that Shinonome Ruri is Furukawa Natsuki in disguise. Although longer in back and different color the front part looks a lot like the hair of Natsuki. Just a guess though, will have to wait until around ch100 or so when Natsuki reveals herself to find out one way or another. Curious to know what really happened to her. Personally I think father meddled or something big happened like was really to pay off Yakuza who wanted to squeeze more or entered Witness Protection and had to vanish without leaving any traces. Natsuki didn't seem to be in it for the money and really seemed to care about him. Also, if just in it for the money instead of disappearing would've claimed some complication or something developed and tried to squeeze more out of him like those paid for friends of his as 20 million Yen is about $200k so seems odd to run without trying for at least a million in US dollars. Besides, I find it hard to believe his father would bring back a gold digger that broke his son's heart just to get an heir. If only wanted an heir than Hime has better chance as MC is attracted to her and a fan of hers while she seems very willing to have a physical relationship with him. That and I wonder if this is suppose to be shock therapy to get MC cured of his gynophobia and being a hikkomori while dealing with his issues with Natsuki with the part about choosing a wife and siring an heir either just a means or secondary objective or smokescreen to conceal primary objective. Well just speculating so hope find out there was a good reason for why she disappeared.
