Just finished reading it and I am still very traumatized because of the two side story chapters. Overall, I loved reading it and I was so immersed in this story. If I'm gonna describe the experience, I'd say it's one hell of a rollercoaster ride. Moreover, like the others said, there are a bunch of twists around the end of season 2, and also around season 3. I think it was around chapter 50 to 70 when I couldn't even bring myself to feel excited from the romance because I can't help but feel anxious of the ominous foreshadowing.
Basically, I couldn't help but feel anxious of Kaidel because after he found out about what really happened during his childhood and how Eleanor is related to it, he acted the same on the outside but he was struggling with his emotions on the inside. He even mentioned to Eleanor how it would be easy if he could sort out his feelings into just black and white. The reason why I was feeling anxious is because he would occasionally do some unsettling stares at Eleanor and his point of view wasn't shown that much. It's really hard to describe.
Anyway, I think everything was settled and they had a happy and satisfying (for me) ending until the side stories happened.
(Ending spoilers ahead!!!)
After everything was resolved, Kaidel surrendered the Hadesreign family name and left with Eleanor. They started living together in their hometown (the place where the fire happened) and they even got married with just the two of them as the attendees. As time went on, everything was fine and they were happy until the problem came. Kaidel aged and Eleanor stayed the same. However, before Kaidel died, he went back to visit Count Hadesreign (now emperor) and the Eternal Sleep reagent was returned to him. He mentioned the following words in a letter that Eleanor found alongside the reagent (gonna quote the whole letter contents since I recommend reading from start to finish T_T):
"My beloved Eleanor, I'm sure you'll be surprised to find this letter and reagent. Just imagining your surprised expression is so lovely. There's something I didn't get to tell you, so I've prepared a surprise gift. Eleanor, to me, the time I spent with you is incomparable to anything else. They were a succession of shining moments. We shared so much happiness and also sadness. The snow fell, and new plants sprouted. We were able to see it all dozens of times. And like that, time continued to pass. Whenever that time approached, you suffered so greatly... that my own heart felt like it was falling to pieces. So that's why... I'm leaving this letter alongside the reagent for eternal sleep.
How did I find this reagent? There's something I didn't tell you. To be honest, a while ago, I went to see the count. No, I should call her... the emperor. I mentioned the reagent, and the emperor returned the reagent that had been in the possession of the demon. And I also saw a familiar face. It was our first meeting in decades, so I was nervous. But it was comforting to see them doing well.
That was how I got my hands on the reagent, but the reason I didn't tell you... was because I wished that you wouldn't drink it after my death. The world is too vast... for you to take this reagent willingly. I wanted you to experience this bittersweet but beautiful world... over... and over, so that you could become stronger. Of course, I'm not asking you to continue a never-ending journey. But I want you to use this reagent, not as a means to forget your sadness, but once you have nothing more to wish for in this world. Eleanor, my love. I pray that you will make it through the pain."
I can't T_T I'm crying buckets as I typed it all out. In the end, Eleanor drank the reagent and fell into an eternal sleep. I was happy, sad, and satisfied with that ending already. Until Noah happened. I'm gonna shorten it as much as possible. What happened was, Noah woke Eleanor up but she's kind of like in a vegetative state. Basically, she's awake but she didn't respond to anything that Noah did. Noah even tried kissing her but there was still no response. It happened for years until Noah ended up pretending to be Kaidel, which brought light to Eleanor's eyes. I'm gonna stop here and I don't want to describe it further because it was so unsettling.
P.S. I should've heeded the disclaimer warning at the beginning of the side stories. "To those who wanted a happy ending, I ask that you close the book right now." Too late for regrets T_T