TP is the only place. Prioritize Spica, as you can use her to farm more DC in the harder maps.
And I suppose the male word for ninja would be shinobi, though technically it is gender neutral.
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Male ninja/shinobi are just ninja/shinobi.
For that matter, ninja and shinobi are just different ways to read the same kanji (originally shinobi no mono, then shortened to just shinobi). The difference is, shinobi is the kun'yomi (native Japanese reading) of the characters, while ninja is an on'yomi (Chinese-influenced reading). Historically, shinobi is the reading used for much of their history, while ninja as the reading is a much more recent thing.