Nuka

I would recommend Sepia Tears, One Thousand Lies and Naricssu if you're looking for free VNs on the Play Store. 
As for those playable on a computer, my top picks would be:
Rewrite and Little Busters - Both have an amazing soundtrack and they give you quite a bit of feels. Rewrite has a bit of a darker theme than LB, since LB focuses quite a bit on friendship. 
Grisaia no Kajitsu - A personal favourite due to its hilarious character interactions and amazing MC. 
Root Double - Something that has a unique 'choice selection system' and the story pretty much keeps you engaged throughout its course. Themes of survival and mystery. 

My train of thought goes like this:
> Little Busters has awesome soundtrack
> Music is justice
Henceforth
> You've gotta play Little Busters sooner or later.
Also, the feelz.
 
A copy of 999 for DS (also playable in 3DS due to retrocompatibility) is probably expensive now. If you have a decent Android device you can play it with emulators like DraStic. If you're willing to get Little Busters, you can also make the extra effort for 999. And the Funyarinpa is justice.

We talk about porn slideshow games.  

Katawa shoujo, most probably. 

Well, after steins;gate, i kind of understand you.
 
That's why, i'm pushing up Little Busters, if you liked Katawa, why not go for the stuff that inspired it. 

I'd suggest bocchi musume (little miss lonsome) even more, then https://vndb.org/v18690, since it's specifically aimed at female audience. You would have to wait a bit, though.

Well it's not random. The protagonist falls in love with the selected waifu and they have consensual sex, sometimes in inappropriate places, because they love each other.
I mean, you read Katawa Shoujo and Hisao pretty much gets raped in one route.

you´re literally asking for shingakkou there. literally. may father august have mercy with your soul...