The scenario I've been considering is in the aftermath of the battle (i.e., sometime between late May and September 1905) where a fourteen-year-old girl buys a manga-like illustrated storybook depicting the Japanese naval victory for her five-year-old brother (when he makes puppy-eyes over it). And if it helps at all in determining the likelihood of this scenario, they live on the outskirts of Tokyo, and she supports them by working in a factory that makes naval uniforms. (The children are Asato Tsuzuki and his sister Ruka.)
I've checked the Wikipedia pages relating to the history of manga, and Googled "Manga--history" and "Manga--Russo-Japanese war," but haven't had much success. What I have seen suggests that this isn't terribly likely, but the scenario appealed to me so much that I didn't want to discard it out of hand based on my (admittedly scanty) reasearch, unless someone told me bluntly "nope, not possible."