So, the incest master decides to make vanilla, time-travel harem?
The relationship dynamics sucks, but i guess that's given if you'll try to switch from porn to actual romance.
Other than that, it's pretty decent.
So basically, in the original world of MC the sporty twin fell in love with him, but she died the day MC would graduate (most likely she was going to confess or at least see him one last time), the other twin then read her diary and gets to know about MC existence, years later she helps some overworked man who happens to be the MC, they get to know each other, she falls for him too, but the day he asked for her hand in marriage she said no since she can't cope with the though of being happy when her sister is dead and even worse, with the man she loved.
After chapter 30 the plot becomes kinda meh
We see wedding of the black haired girl with some other dude, she throws the bouquet and lands in the twins hands, they ask MC to make them both happy and he accepts?
Like why not THEIR wedding or sum? Why waste the chapter on some other couple?