Tohru is a classmate of Netto's, though he does not come in the series right away. His Net Navi is the adorable Iceman, who also helps out in maintaining his father's Water Plant. Tohru is a quiet kid and very responsible, he realizes that Iceman's duties are very important, and puts them ahead of Net Battling.
Later in the series, it becomes a running joke that poor Tohru is always left behind when something "fun" is happening.