I'll be honest, I'm kind of struggling with the 'name on accomplishment,' but I think if I had to choose, it really would be Kim-001. Creating Kim-001 was such an easy task for me to do, but weaving her into such a big and pre-established world like Halo and make her feel natural in that world was actually quite a challenge, even though I know the Halo universe fairly well. I always knew that I wanted her to be a Spartan (spoiler I guess), but I struggled with that concept and how I could possibly have a Spartan be involved so early in the story of Forward Unto Dawn and how I could create a Spartan and have them be paired up and have a 'romantic' relationship/connection with John-117 when the Master Chief is fairly standoffish and emotionless until way later on in the series. So, taking the time to build Kim-001 up, including bits and pieces from the books or games in (like a small scene that I've come up with for when Kim-001 and John-117 reunite at the Academy) really solidified Kim-001 into the world for me and made me believe that I could really pull off a John-117/OC relationship.