What sets [New Story Of Aura Battler Dunbine] apart and makes it notable is its production style: The mecha are mostly drawn with background drawings rather than animation drawings. Typically in anime you have the animation drawings, drawn on cels with flat colors, overlaid over the backgrounds drawn by the art department. Sometimes if you need a bush or something "in front of" a character, you will have something called a "book" - basically a piece of background art drawn by the art department, but with its outline cut out so that it can be placed on top of the animation drawing. This makes it seem like the background surrounds the characters.
What seems to be happening in New Story is that they've drawn all the mecha as books. Either this, or they invented some new technique to allow them to paint on cels the way Tadanari Okamodo did in The Soba Flower of Mt. Oni (which I obviously doubt). So you basically have the mecha drawn as background art in the midst of a shot in which all of the rest of the character and effect animation is drawn on cels, which have a completely different color scheme that makes the difference quite stark. It actually contributes well to giving the OVA a more fantastical atmosphere befitting the material. We're accustomed to seeing mecha in the simplified forms and flat colors of cel animation, so it feels sumptuous to see the mecha rendered this way. Rather than a toy advertisement, it actually feels like a fantasy world.The monolithic, plodding movement that results from having to use a single drawing also contributes to imparting a feeling of the vast size of the mecha.
Above you can see some examples of the art mecha drawings interacting with the cel drawings. It makes for a slightly unsettling experience, as it upturns how we've been trained through experience to parse the animation screen. Normally the cel drawings can affect the backgrounds, but not vice-versa. Here, the background drawings are affecting the background drawings. For example, in the left drawing, the art mecha crashes into the art wall, producing cel bricks and dust.
This is an unusual choice for a mecha show, since the whole point of using animated drawings is so that you can simplify the drawings to complete the animation in a shorter time. It's not unprecedented, though. Nausicaa was the show's big influence in many ways, so it's possible that the Ohmu were the inspiration behind this technique. It also brings to mind the way the castle in Howl was animated with patches of background art to give it that special look. Coincidentally or not, the photography director of most of the great Sunrise OVAs of this period, including New Story, was Atsushi Okui, the guy who went on to come up with that special way of animating the castle in Howl.
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