I am an avid reader, and I may have the perfect set of novels for you.
I recently discovered my new favorite author, Ken Follet (pron: foi-et), and some of his remarkable novels.
I have only just finished another one of his books, "Place Called Freedom," which I highly recommend to anyone ~18 plus. His novels are very mature, sparing no detail from brutal encounters to passionate love-making (and the occasional mixture of the two), but the dialogue and plots of the wonderful worlds he creates are instantly captivating.
My favorite books of his are a short series based in medieval England, and spanning the lifetimes of their main characters and ultimately many generations. Beginning with the first novel "Pillars of Earth" set in around 1100 a.d, the series follows not just one, but many characters through their lifelong journey from early childhood to their emotional endings, and occasionally, an early grave. Spanning a great deal of time, the story emerges again a couple centuries later with "World Without End." There are many twists and curveballs that keep you on the edge of your seat throughout both novels, and based on your need for instant immersion, I feel that these books would do just the trick.
I can't stress enough that this is VERY far from anything Manga, but it is something I imagine anyone asking for reading advice on a gaming site to thoroughly enjoy.