Like father, like son, huh...
|― Isanari Uesugi|
He has a distinctive golden, spiky hair and is mostly seen wearing a sunglass on his forehead. Fuutarou five years ago also shared similar facial traits to Isanari.
Isanari has a wild character. Fuutarou five years younger is said to share the same personality as his father, notably both were bad at studying.
Isanari and Papa Nakano seem to have some history. It was through Isanari's connection with Papa Nakano that his son, Fuutarou, became a tutor for the Nakano quintuplets.