Sleeping deeply and waking up occasionally. He lost quite a bit of his powers. Now he's more towards his beastking lineage rather than his elf lineage. (no more silver hair >A<)
I forgot the exact moment the MC met his sister but I think she revealed herself near the end of a mission and then he found out. and no she doesn't have an elf with her as of yet.
Long post in coming so I'll just put it in the spoiler tag to save space. Lots of quotes to try to answer from memory. Yes he gets a white robe at S2. In my memory he never leaves the dorms because it was like a special permission and he never moved out.
The memory that got sealed was the one that 'remembers' the 100 sentences of Elven spells. His senior used it once to save the MC while trying to hold back the ghost king(ultimately sacrificing his life). It left a lasting impression on him and the MC used it(he remembered every word) to combat the ghost king forces when they came to take over the school. (and managed to get back his senior's body too) In order to get his soul back, he gave up the 'memory of the 100 sentences of Elven spells' as a price. But he gets it back one at a time later on when he finds pieces of...something i forgot what that was scattered around. The partner of the one that took the price agreed to give him back the memory a sentence at a time for every piece he finds.
Yeah, as he awakens his powers and go through all that life-threatening experiences he's starting to 'turn black' and less spineless. The end of season 2 literally had him controlling one of the ancient dark weapons that his race would one day use to 'reset' the world from light to dark. (which is why his race is one of the most hated in the (races of)light world)
His sister gained the medical knowledge of the ancestor (as he was a great herbalist). I'm not sure about strength..maybe spells? His cousin is the current patriarch of the clan and inherited the memories of the ancestor. MC inherited the powers of the race which is one of the most hated/strongest racial trait. Some of the other people of the clan has it but it's not as strong. Everything he thinks of/believes in will turn real. He believes he's very unlucky which is why it always becomes real. So when he looked at the dead body and thought that the Ghost King looks like he would suddenly wake up and revive, it did. Good thing is, when he prays for success, it happens with great effect~~ not that he does it often...only under strong influence of the situation or prompting from people.
Everyone originally just called him prince because of his strength and stuff (like a title). But after they found out about his bloodline, he's a real prince from both his parent's lineage. But the identity of prince goes to a few characters in it because they're basically all coming from different clans that has royalty in it. (Which means the line of the patriarch.)
MC was all shocked that his sister is a purple robe and part of the 'patrol unit' that everyone in the guild fears. (cuz that unit stalks people on missions to write reports about how they handled the situation so if they did badly they would get demerit) His sister knows. Just that the clan didn't want to tell him before in order not to pull him into this world.
Actually Japtem has quite a number of chapters hidden away in their forum and ToC that wasn't announced or submitted to novelupdates. (A few volumes worth.)
Usually it's just his senior that smacks the MC's head or the sister. It's more like he got annoyed by the weak whining(can't blame him for screaming at narcissistic clock faces that try to kill people or other weird stuff) and partially to snap the MC out from 'thinking' about things (in case his powers make it real). It went as far as the senior casting a spell so that he can listen to the MC's thoughts (which is a lot of whining negativity or weird ideas). This shows you how dangerous the MC's powers are.
Wow so much info popping up suddenly lol thanks @Haigi (still think thats a bad attempt at jap humor lol) Anyway yeah I knew the story was still ongoing as I checked the raws and the comments there complaining how the author was slow (they always complain on any story thats slightly slow, rant culture lol)
Hopefully it get translated again someday as the girl community grow and will probably like it better than the male one x)