That bar represents your Karma in the game.
Red being bad Karma, Blue being good.
The middle being Neutral.
I plan for it to affect the endings, and perhaps events in the game's story.
Also the route you're on is determined by who you've picked on the selection screen.
Planning for an Ayano & Reina choice in the future.
Thanks for clearing up the confussion, thought at first red side (bad karma) was more dominant and take things on alone as it felt like that, while blue side (good karma) felt more submissive and people riding over ya as well you can't do things alone and ask others to help.
About the girls I love Sanae and Reina the most, Sanae seems a kind hearted warm motherly women, Reina seems more a strong but still caring woman who appreciate men who aren't heel lickers. So a Reina path i sure would love too.
Sachie I don't know feels somewhat two faced, kind and warm caring, but suddenly behind closed doors she seems a dominatrix who don't like dominant men and love to break them.
And Ayano, although she is the mc love and Reina's sister, she somewhat feel like a religious zealot that see sex is wrong as pleasure and only for reproduction, also she does her duty as wife, except in bed she is a frigid cold ice queen unless it behind mc back when she solo.