Space cruiser Triant 2 from the free planetary association established a primary contact with an unknown life form while executing its mission. An organism entered the ship and started to attack crew members. No weapons could kill it and the crew had to separate the hull of the ship and abandon it. Then the military ship found the drifting hull, but men were wiped out... First and second missions to annihilate the organism were miserable failures. The four remaining members of third mission had to destroy the ship by destroying it with missiles.

With that the incident was supposed to be over...

[From vndbreview]

Sequel to PC-9801 game Blood Seed from Great