What is the meaning of へ or への in this case:
へ in this case is expressing direction, similar to 海へ行く, though in this passage the direction is not physical, it is expressing the 'direction' of popularity (人気).
の is being used to make the part before it "...漫画" modify the part after it "人気。。。"
So "漫画への人気" could be loosely translated as "Popularity of Manga".
Here is an article I wrote about this topic with more examples.
UPDATE: Below is my rough translation of the passage in question for reference:
In China, building on the already high popularity of Japanese Anime and Manga, "Your Name" has quickly become a hot topic in places such as the Internet, and there are some movie theaters where tickets are already sold out and most seats are filled.