Wiki states that:
Del Toro envisioned Pacific Rim as an earnest, colorful adventure story, with an "incredibly airy and light feel", in contrast to the "super-brooding, super-dark, cynical summer movie". The director focused on "big, beautiful, sophisticated visuals" and action that would satisfy an adult audience, but has stated his "real hope" is to introduce the kaiju and mecha genres to a generation of children.
While the film draws heavily on these genres, it avoids direct references to previous works. Del Toro intended to create something original but "madly in love" with its influences, instilled with "epic beauty" and "operatic grandeur".
Does that mean that there are indirect references or influences, aside from the whole generic idea of kaiju (giant monsters) attacking humans and mecha (giant robots) used to battle them? If so, what are those references or influences?
I'd prefer the answers to be concentrated either on wide tropes, OR well-known "important to the genre" references, not simple "Pacific Rim had XYZ, and this random monster movie had XYZ as well, so here's an influence"