IRoHa de Sudoku!

Sudoku (Number Place) is a puzzle game played all over the world. The rules are simple: Fill all cells in a vertical row, a horizontal column, and a 3x3 box with 9 different characters so that there are no duplicates. In this application, instead of the usual Sudoku numbers, the nine Japanese hiragana characters "い(i)", "ろ(ro)", "は(ha)", "に(ni)", "ほ(ho)", "へ(he)", "と(to)", "ち(chi)", and "り(ri)" …