
If I want to read the novel, anyone know which chapter to start at to continue from where the manga is up to?

Here: https://novelplanet.com/Novel/I-Alone-Level-Up/c107-109?id=488155
These chapters are grouped together for some reason but chap 107 is leading up to (and including) the big demon fight so here is a good place ٩(๑❛ᴗ❛๑)۶
Henry is an idiot, but Seth knew from the beginning what he was getting himself into, and he still knows that Henry was always into someone else and he said he didn’t care...