A few things that you must improve since you are doing a rewrite. FIrst. More interactions between Rudeous and MC, they are brothers, reincarnators of the same world, they should have a lot of stuff to talk about, converse with eachother about their findings in magic and all. Rudeus may be weak physically, but the dude has a lot of imagination for magic. It would be a huge shame if he ends up the same as original power wise. Also you made rudeous be seen as a minior character that was just to be the brother of MC. Rudeus is one of the MAIN characters, so he cannot be put as background.
Another improvement would be that you DONT stick so much to the original novel, i mean, there were whole chapters that were almost 90% the same as the novel, thats not something you should do as the butterfly effect of Rudeus having a reincarnator twin brother are HUGE.
The mc interactions with Glisaline were odd because you listened to a random dude that did not like she did it with MC father years ago before he was born.... and speaking about her, Ghislaine, she is in her 30s by the time rudeus meets her, already past her prime age, so try to make her younger somehow..... Now about this, you should know or at least MC should know that aging is because cells cannot multiply themselves fast enough. As one grows up to being an adult, they multiply cells extremely fast and this slows down after they reach the 100% adult state, from then on, cells divide slower and slower as you age, this is why people look old, as cells cannot replace the skin cells fast enough and each consecutive cell is weaker than the previous one.... So, to regain "youth" you must make the body cells be reinvigorated so that they can multiply themselves as fast as when one reached the prime age (21 or so). This way one would regain their "Youth". MC could make a spell to analyze the cells of Sylphy for example and test with the youth magic with animals, to make a healing magic that reinvigorated cells from mana. The king healing magic can regrow an arm, that healing magic is already doing what mc needs..
ALso, try to not make it so forceful the whole thing with Lilia and teach Roxy some science stuff, like why fire burns for example. She has no idea why, she just accepts it, it irked me a lot that mc did not teach that stuff that would improve their magic by a huge margin.
About Eris family, to save them you must think very well how you will do it. You must protect FLUFF!!!!!!.... As for paul dying... well it helped rudeus mature a lot, but thats for when he was alone, now he has MC to get a partner to shoulder things with. Speaking of the teleportation calamity, due to mc, it no longer can be the same, meaning, that Zenith may not end up inside the crystal in that laberith, etc. You must also consider the whole Hitogami thing, as it may be possible for MC to kill him, there is also the issue with Dragon god Orsted. For him, MC and rudeus are an anomaly.... what else... oh yea, POWER UP ROXY....
Lastly, it bothered me that mc created new magics, but did not teach them to rudeus and viceversa. I mean come on!... 2 dudes from earth and they dont brainstorm magic together to make new stuff!??!.
Power up roxy, enough said... Also make juicy XXX chapters.
