If you max out the base abilties plus a few tank abilities (armor, health, resurrection), then place the tank roughly in the lower-right corner, you can win without moving or firing a shot from then on.
1) Start out with all three on the grass in panel 1 and on the ground in panel 2.
2) Move both boys onto the dirt in panel 1.
3) Move the green boy into the cage in panel 2.
4) Have the girl kill the purple boy in panel 2.
5) Move the purple boy into the cage.
6) Move the green boy so that the girl kills him.
All three will have hearts in panel 3.
 "Crystal Story II"){kind=icon}
 "Hands of War 3"){kind=icon}
 "no-one has to die."){kind=icon}
 "Wake Up the Box 5"){kind=icon}
 "Zombotron 2"){kind=icon}
 "W-Zone"){kind=icon}
 "Flagstaff: Chapter One"){kind=icon}
 "Versus Umbra"){kind=icon}
 "Storyteller"){kind=icon}