What does Natsumi mean in Japanese?

Answer 1

Without the exact kanji of what you mean it's impossible to define a Japanese 'name', they have diff kanji, each kanji has many diff usages and readings, each of those readings in combination with others could or could not be used and mean something, and when they do believe me it's so hard it's well around impossible to say this means that.

Just one interpretation of a random kanji selection for Narumi could be ' beauty of honesty'

Answer 2

Most names have several spellings in Japanese, so unless provided at least a certain character whose name you refer to, or the 'kanji' with which the name is written with, a certain answer is impossible. Some possible ways to write 'Natsumi' are:

夏美 : summer beauty

夏実 : summer truth/fruit

七海 : seven seas/oceans