The PC married these girls' mother, so he is not directly related to them.
BUT! There are 3somes and whatnot that have both girls together, and sister-sister is still incest, hence the tag.

Also, really good game that turned into a decent hentai-anime (with both parts out at the time of this writing.)

Edit: I almost forgot, the mind-control / mind-break comes into play with the drug he uses, which is pictured on picture 170. Don't know much about it, but I do know he utilizes it in some way throughout the story, and it has awesome-sauce powers (that makes me want the drug myself...)

Base +4, Shadow Infinity +9, yoyo546 +12, Tachibana +9, Huehue2 +7, zhangetongkuai +13, Silent Soprano +6, MASigma +11, sadoshi +5, zerohero2 +9, Robdog01 +1, Leonaides +7, Misaki1995 +1, and 7 more...

PG 166 is that the mother?

Base +4, lygarx +8, ScrawnyJohny +6

Does marina has a boyfriend in the game?

Base +5, ArnasB +7

Marina's BF is NTRed

Base +5, diehctaz +6, ArnasB +7, scrappy135 +7, ScrawnyJohny +6

hmmm so this's Netori huh ?

Base +9

The fact that the mother gets ONE picture is shit!

Base +5, ScrawnyJohny +6, Drode +9, marconii2002 +21

[ブルーゲイル] 鬼父～愛娘強制発情～
[Blue Gale] Onichichi ～Manamusume Kyousei Hatsujou～

Release date: 2008/10/24

Link (VNDB): https://vndb.org/v3343

Base +17, ScrawnyJohny +6