I don't think Hara will gloss over the Dark Sei stuff. While it's true Hara won't be painting Sei in a murderous light, nothing is stopping him from making it seem like Sei making a "sacrifice" for the good of the nation. During the Second Seikyou rebellion arc, Seikyou mentioned how big of a sacrifice Ei Sei will have to make in order to unite the kingdoms. Murdering Lao Ai and his half-brothers would be the sort of sacriifce that was alluded too. If Sei is directly involved in their deaths, then we'll see him brooding for a while. If not, we'll see him being angry but then being told "You are the king now. Steps like these have to be made in order to keep the nation unified and in order to reach your goals. An example had to be made so no one will ever dare try to betray you again."
If Hara glosses over the real shit that happened in this arc, then he'd be doing a great disservice to the manga he has been writing for all these years. Ei Sei was a great king who was able to do things that no one else ever dreamed about, but he was also a merciless king who killed anyone who stood in his way. All of his qualities, both good and bad, were required to bring some semblance of peace and unity to China.
