The name NASU no Yoichi is not seen in Azuma Kagami (history book) and other historical materials of the period, so the assessment of Yoichi's performance relies heavily on the descriptions written in Heike Monogatari and Gempei-Josuiki as military epics (therefore, the existence of Yoichi has not been proved academically).
吾妻鏡など、同時代の史料には那須与一の名は見えないため、与一の事跡は軍記物語である平家物語や源平盛衰記に伝えるところが大きい（そのため、学問的には与一の実在すら立証できていない）。