Daigoro Okuma is student of Katsu Itsuko's father Katsu Kaishu who disowned him as student because he was cowardly. Kaoru Kamiya took him as an apprentice at the Kamiya dojo where Daigoro learns swordsmanship from Kaoru.
He makes friends with Yahiko who is fond of Daigoro's studies and later on even starts reading science books lended from Daigoro. It seems he has romantic feelings for Katsu Itsuko and highly respect Katsu Kaishu.
One of his personal treasures is a book by Jules Verne given to him by Katsu Kaishu who said it is a must for someone who wants to explore science.