It's OK to Purge the World if it is for my Little Sister

Mina, a Lieutenant of the Space-Time Vanguard Unit arrives from the distant future to interrupt Ichikawa's peaceful life with some upsetting news of how the world would end-up if he continues to pursue his affection about his little sister. The sound of the grim news doesn't seem though to deter Ichikawa resulting in Mina having to take any and every possible action to convince and if necessary seduce him!