After the 41st Summer Inter High
Sadatoki is introduced before he enters Sohoku High, invited by his brother to visit the club room in the fall after the first Inter High. While the team is confused at first, Sugimoto insists and shows off his younger sibling's strength, loud voice and skill. In the anime though, he was shown to had ripped the door clean off the hinges as it was locked.
In the anime, Imaizumi questioned his balance and dexterity, hence testing him to ride on rollers before joining them in practice, which Sadatoki passed with ease, even when he had never been on one before.
While Sadatoki seems unskilled in actually racing at first, it is shown that he is more than it appears to the eye.
Year Beginning (First Year at Sohoku High School)
On the First Year Welcome Race, Sadatoki aids his older brother that decided to race on it as a second year, so he could have a better record and join the Inter High as the 6th representative for Sohoku High Bicycle Club by winning it. Despite all his effort, his brother failed to win the race, placing 2nd.
Despite not finishing the 1000km and not being able to join the Inter High, Sadatoki managed to do 820km on the end of it, a better result than his older brother when he was a first year (650km).