I'm writing my story and I'm using an order of plot events I created. Now I'm in a part where the story takes a bit of a lighter tone. Now is my chance to introduce new friends to the main character so that he establishes a strong relationship with them. They're not very relevant for the overall story I'm going to kill off his friends a bit further, but I need to know how to write the secondary characters lovable enough so the reader is "affected" or just moved by their deaths. My goal is to take the story's tone and make it have a dark background while scene by scene the reading is a bit light. I need to make that it of a contrast. I'm writing a fantasy and it's just a war going. Long story short, the main guy goes to boot camp and meets his companions. After their first mission everyone dies. How do I write the characters so that you can relate to their deaths?