@Greg_Dickson I'm not speaking specifically about your story, Greg. I'm sure you'll be able to pull it off just fine! It IS possible to locate the death of secondary characters at the start of a story, and then use flashbacks to build them up! It's a method of storytelling that works for other things as well - like putting a big, flashy fight-scene at the start of your story, and then cutting back to way, way earlier in the timeline and building back up to it, etc.. If you handle it well, it can be a very good hook for a story!
And I'm not passing judgment on your story in particular. Please, please don't feel personally insulted by this, that really isn't my intention at all. I haven't read your comic, so I literally cannot have an opinion on how you handle it.
When I brought this up, it was to point out the times when it is done badly. There are PLENTY of stories in which revenge over a cardboard no-personality secondary character is a hero/ine's entire motivation, and that's the bad thing about it. I said I'm wary of the trope, because it's often mishandled - but not always.
But my personal opinion on a trope shouldn't keep you from using it! For example, I personally despise love-triangles - but that doesn't mean love-triangles should never be done, or that the people who do them are bad writers. It just means that I've read too many stories in which love triangles are badly done, so I personally choose to stay away from it. Using the death of a character to motivate another isn't inherently a bad thing - revenge is a powerful motivator, in real life as well as in fiction - but it can be handled badly, and it very often is.
I'm of the opinion that each decision you make with your story should be made with some kind of intention in mind - and if killing one character to motivate another is something that will make your story work the way it's supposed to, then by all means, do it! If you can lend that death some emotional weight and meaning after it's happened, then that's great! My post was mainly about those instances when the creator doesn't put in that effort, which unfortunately happens a lot.
ETA: I just want to make it doubly clear - when I used the word "you" in the main body of my second post, I wasn't specifically referring to you, Greg. I was referring to storytellers and/or readers in general. English is my second language, and sometimes I'm not as clear/understandable in text as I would like to be, and I should maybe have structured that post better.