Himawari! S02 E02 If You're Going to Eat an Herb, It Might as Well Be Poison

Himawari was saved by a ninja when she was little, and has wanted to be a ninja ever since. On her first day at ninja school she meets Hayato, a non-ninja teaching to pay off his debts. Interestingly, he has the same mark on his neck as the ninja who saved her.