Well, 'Monogatari Series' is a notable Japanese fantasy light novel. It has a complex and unique narrative structure. The story involves various supernatural elements and the characters' relationships are deeply explored. 'Log Horizon' is another good one. Set in a virtual world similar to an MMORPG, it focuses on the social and economic aspects of the in - game world as much as the battles. And 'Kagerou Project' is quite interesting too. It has a time - loop and mystery elements, with a cast of characters with different abilities in a fantasy - like setting.
One great Japanese fantasy light novel is 'Sword Art Online'. It's set in a virtual reality MMORPG world where players are trapped and must fight to survive. The story has great character development and exciting action scenes. Another is 'Re:Zero − Starting Life in Another World'. It follows Subaru as he is transported to a fantasy world and has the unique ability to return by death, which makes for a very engaging plot. And 'Overlord' is also popular. It tells the story of a powerful wizard who gets trapped in a game world as his character and rules over his territory.