Ladder Structure

This Visual Novel has a type of branching system that works like a "Ladder".
Basically, instead of the routes branching off from the end of the common route/prologue, they split off during it.

The reason it is called a "ladder structure" is because you can consider choosing the hero(ine) paths along the way to be "getting off the ladder" and staying on the common route as going to the top (the final route on these "stairs").

G-Senjou no Maou and Grisaia no Kajitsu are the prime examples of this structure.
Other examples of this type of structure in VNs: STEINS;GATE, Aiyoku no Eustia, Tokeijikake no Ley Line -Tasogaredoki no Kyoukaisen-, Amatsutsumi, Sen no Hatou, Tsukisome no Kouki and sweet pool.