I get why you're curious — that very specific visual niche has its own little ecosystem. From what I've seen, mainstream anime that actually spotlight giantess butt-focused scenes as a fetish are quite rare; when size-change shows happen, it's usually for spectacle or horror rather than erotic emphasis. A good mainstream example of large humanoids is 'Attack on Titan' — the Titans are huge and the animators sometimes frame parts of their bodies in close-up for shock value. That occasionally results in brief shots that some viewers read as fetishized, but the series uses those images to unsettle rather than to titillate.
If you want stuff that leans into rear-focused visuals more blatantly, look in two places: shows that emphasize butts without necessarily being about giant women (for example, 'Keijo!!!!!!!!' practically centers its whole premise on butt- and chest-focused action), and the adult/doujin world where giantess is a bona fide subgenre. In the latter you'll find OVAs and fan animations that explicitly cater to giantess themes — those are where you'll see prolonged, prominent rear scenes because they're made for that audience. I also sometimes spot one-off gags in long-running shounen shows (size spells, transformation sequences) where animators will playfully exaggerate body parts for a laugh or shock.
So, short version from my side: mainstream anime with giant women include 'Attack on Titan' and series that feature giants or size magic, but the sustained, prominent rear-focused giantess scenes live more in adult doujinshi, niche OVAs, and fan animations. Personally I find the contrast between spectacle and fetish interesting — it says a lot about how animation can be read very differently depending on the viewer.
Giantess art is such a fun niche to explore because it blends scale, perspective, and creativity in such a visually striking way. When I first tried drawing it, I started by studying how proportions shift when something—or someone—is massive compared to their surroundings. A good trick is to sketch the environment first—tiny buildings, cars, or trees—to establish the 'normal' scale. Then, lightly outline the giantess's feet or hands interacting with those elements. Her toes might crush a street, or her fingers curl around a skyscraper like it's a toy. Don't worry about details early on; focus on the dynamic poses and the 'wow' factor of size contrast.
Once the rough composition feels right, I refine the giantess's form, paying attention to how her body distorts slightly due to perspective (e.g., foreshortened limbs). Clothing wrinkles and shadows become way more dramatic at that scale, so I exaggerate folds where her legs bend or fabric drapes over buildings. Lighting is key too—casting a shadow that engulfs half the city sells the illusion. I love adding tiny, panicked humans for scale humor, like ants fleeing her footsteps. It's all about balancing the fantastical with just enough realism to make it immersive.