どんな題材で和風絵手紙を描きましょうか

Sure, here is the Midjourney prompt optimized to create a traditional Japanese letter style illustration featuring an eggplant, pumpkin, and cucumber:

md
1A traditional Japanese letter style illustration with a focus on bold featuring an eggplant, pumpkin, and cucumber. Japanese ink wash painting style, Sumi-e style, Watercolor style. Simple and expressive brushstrokes, expressive lines. The outlines of the motifs are drawn with thick brushstrokes. The drawing has the charm of being sketched with the non-dominant hand. Soft, muted colors, Minimalist composition, Plenty of white space, Off-center subject. Wet-on-wet technique, Spontaneous and natural-looking --s 150 --style raw --no realistic, text, monochrome