Mondaiji: Horrors Beyond

We've all heard stories of the Necronomicon, a lost grimoire holding countless ancient spells and dark magics to summon forth monsters and unimaginable archaic deities. A book having been sought after for countless centuries by both humans and monsters alike. However, that very book now rests in the hands of a young man living in the city of Tokyo. Kenichi Ren knew that his life was never going to be the same ever since he met that strange man that handed him this book, but what could he do about it now? Well, perhaps there may be reason for his life when a letter suddenly falls from the heavens. A strange letter speaking of a place called... Little Garden?