Tetsujin 28-gou (2004)

In post-WWII Japan, Prof. Shikishima has built up Shikishima Industries to be a technological powerhouse, working on developing robots. However, at the heart of their success lurks a dark secret from the war, something that cost the life of Prof. Kaneda, the mentor of Prof. Shikishima. Now Kaneda's son, Shoutarou, is about to learn the truth, and it will change him forever.
(Source: Anime News Network)