EXPLANATION TIME:
Jack is a gifted. The gifted were a bunch of babies born into such conditions that altered their genetics to make them powerful, and able to use certain weapons. All of the others were killed off by a group called
'The Movement'.
The movement is a bunch of vampires bent on turning humanity into the undead. Jack was captured and tortured, and thus his powers were drained, and he's become weaker than a normal human being.
Jack decided that he should go back in time using a machine built in the near future, and kill himself before the movement could drain and use his powers for evil.
Although, by shooting the robot this time, he caused the past to be altered, and the whole course of his capture was changed. Instead of killing himself like he had planned, he's going to protect his younger self, and find somebody able enough to be his younger self's guardian until this whole thing is over.
Back to kira's house:

(The party focus is going to keep jumping around a lot until they meet up eventually)