Takeru

Takeru is Susa and Kushinada's son. In The Lost Age, Kushinada mentions that her son will be called Takeru and will rush to Felix's aid when needed.

In Dark Dawn
Following a premonition from his sister, Himi, Takeru leaves Yamata in order to help Isaac. This occurs prior to player's arrival in Yamata, and thus, he is not actually seen in-game in person, but is mentioned in conversation. But this could hint the possibility of him becoming a playable character or at least finally seeing him in person in the next Golden Sun game.