What this song renders
The Heike Monogatari is the only premodern source that names Tomoe. Its description in Book 9 is famous and worth quoting: she was ‘especially beautiful, with white skin, long hair, and charming features. She was also a remarkably strong archer, and as a swordswoman she was a warrior worth a thousand, ready to confront a demon or a god, mounted or on foot.’ That single passage is the bedrock of every later treatment of her.
Of her childhood, parents, and training there is essentially no historical record. Some later traditions name her father as Nakahara Kanetō, foster-father of Yoshinaka — which would explain her access to the Kiso branch household and to military training. This is plausible but not contemporaneous.
The song renders the formation the Heike’s description implies: the years that produced an archer worth a thousand. The seven-year-old with the bow, the oath under the cedar, the moment Yoshinaka recognised what was in front of him — these are the album’s reconstruction, not the chronicle’s record.
The Heike’s description of her skill and beauty is the only firm anchor. The childhood, the father’s eye, the cedar oath are the album’s. The fact that an onna-musha worth a thousand men existed at all is what the song treats as the documented miracle.