About Grisai no kaijutsu sequel

in the grisai no meikyuu there's a story about sequel of grisai kaijitsu which also tell about yuuji's past, the question is:
is that story is basically linear one? since the walkthrough tells that the heroine's choice only available at the after story and the sequel seems like the 'true story' which focused only to the story instead of the plot, is my assumption right?

also, is the grisai rakuen is also 'route-less' story? :wryyy: