Hakkaku - The Tale of Undercrust - The Last 7 Days of Hasumi + Full Save (eng) - Adult Sex Game

Manual translation

Hasumi meets an android who claims to come from the future
in a smattering of language, making her skeptical.
In order to avoid a meteorite impact that is scheduled to befall
seven days later, the two goes deep into a huge crater lies
at the foot of Mount Fuji. Herds of weird creatures live in
the underground world which, perhaps, will have either
a girl vigorously brandishing a sword or......