Pretty convinced this is what I am going to make with the Arthas model. This story isn't made up, it's actually from the Arthas: Rise of the Lich King book. You may have to do a little bit of imagination between some frames.
To be more specific with the story here, Arthas encounters Matthias Lehner, a manifestation of his former self, representing his humanity. Within Arthas's mind, there is conflict between he and Ner'zhul. Ner'zhul is telling Arthas to kill the boy, and Arthas tries to resist. Arthas ends up killing Matthias Lehner, and to try to cease the Lich King from persisting, Arthas kills himself as well. On a side note, the book mentions their souls are both absorbed into Frostmourne, as with anyone else who gets killed by it. Ner'zhul then takes complete control of Arthas's body, and goes into a deep sleep for 4 years, bringing it to the start of WotLK.
My depiction of Matthias Lehner is in the top right frame. I attempted to make a young version of Arthas before he became a Knight of the Silver Hand.