I'm not entirely sure as I haven't read this particular light novel specifically. But generally, a title like this might be about a character expressing their love or strong liking towards another character. It could involve a story of a person's feelings and the relationship that develops from there.
Since I don't have first - hand knowledge of this light novel, it's difficult to say precisely. However, considering the words 'tantei' which means detective in Japanese and'mou shindeiru' which means already dead, it could be a story where a deceased detective has some unfinished business in the world of the living. It could be full of mystery, with the detective using his or her skills from beyond the grave to solve cases that were left unresolved during their lifetime. There might also be complex relationships between the detective and the living characters, and the story could be set in a fictional world with its own set of rules regarding death and detective work.
I'm not entirely sure if it's extremely popular on a global scale. However, in the realm of light novels, if it has a captivating plot about goblins being strong or having some sort of interesting power dynamic, it could be popular within the niche community of light novel enthusiasts who are into fantasy - themed stories.
You can try looking for it in local bookstores that carry a wide selection of light novels. Some large chain bookstores often have a section dedicated to Japanese light novels.
One possible theme could be unrequited love. The title gives the impression that one character has feelings for another who might not be aware or reciprocate right away.
I'm sorry, I'm not very familiar with this light novel specifically. But generally, a light novel often has unique characters and an interesting story. It might be about some kind of relationship between the characters where one has an unexpected or special feeling towards the other as the title seems to imply.
Since I don't know the exact 'mou mou novel', it's hard to say precisely. However, some novels are special due to their cultural significance. If it's from a particular region or era, it might offer insights into that time's values, beliefs, and way of life. For example, it could show how people in a certain society dealt with challenges like poverty or war through the stories and characters in the novel.