They have a child before they are ready, when war, rather than peace, is a constant of life.
Keta is such a quiet baby that they find themselves forgetting her for hours before guiltily recalling that they are parents. They meet this as they always have any challenge, head-on, she with stoic determination and he with grim enthusiasm.
Dark brown hair blooms on their daughter's head. This disappoints Hashirama. Flowers do not turn toward her touch. This disappoints Mito. Her voice is petal-soft. This disappoints the Senju, who follow nothing less than rooted strength.
There is no time to wallow in disappointment, however, not after Uchiha Madara offers his hand in cooperation instead of conflict. Senju Keta grows up in the prime of her parents' distraction and tries very, very hard not to disappoint herself.
It is when war starts again, ironically, that she is remembered. Her father watches her sew a man back to life without hesitation, her chakra jumpstarting his pulse. And when the next man is too broken, his pieces mangled beyond the saving of her nimble fingers, she feels his large hand on her shoulder for a second on the battlefield, smoothing away her helplessness and inadequacy.
"You've done well."
She closes her eyes and allows herself to believe him.
Notes:
A close scrutiny of the timeline reveals that Hashirama and Mito must have had at least two children, one before the founding of Konoha and one after. In keeping with ridiculous Senju naming traditions, Keta means a beam or a column, usually referring to the wooden cross-beams of a roof.
Writing this drabble really brought out the hypocrisy of the Senju, who value battle-strength as much as, if not more than, the Uchiha. It must be difficult to be the unexceptional child of exceptional parents, especially one in a powerful clan like the Senju.
Oops. I'll stop before the notes get longer than the actual drabble.