irb(main):004:0> x="ん"
irb(main):005:0> x.succ!
=> "ゔ"
irb(main):006:0> x.succ!
=> "ゕ"
irb(main):007:0> x.succ!
=> "ゖ"
irb(main):008:0> x.succ!
=> "ぁぁ"
irb(main):009:0> x.succ!
=> "ぁあ"
irb(main):010:0> x.succ!
=> "ぁぃ"
irb(main):011:0> x.succ!
=> "ぁい"
🤔