>>8
Your theory is as valid as this: With the 12 volumes I have on hand and the three volumes there, that's a total of 15 volumes combined. I have no doubt that this is a set of 15 volumes. The shikigami of the outside world are the same as the ones in Gensokyo after all. With computers, F represents 15 and F is the state wherein everything is compounded. It was written that when everything becomes F, the highest value is held.
I think that it's natural for 15 to have power. Even in ancient times, 15 meant perfection in this country. The same reason the full moon is also known as the fifteenth night. Computers must be familiars that have resulted from the ideas of the East and the beauty of the moon.
Marisa asked me what I was thinking about as she lined up the three books.
Through Marisa's nonchalant actions, I realized something else. The numbers on the books, "13", "14", and "15", when lined up, makes 131415. If the 1 in front is removed... it then depicts the number that represents a perfect circle, 3.1415. This also means a full moon. And thus my theory that the familiars of the outside world use the power of the moon becomes truth.