Gemfile

source "https://rubygems.org/"
gem 'romankana'
gem 'moji'

nihongo_to_roman.rb

#!/bin/env ruby
# encoding: utf-8
# Author: kimoto
require 'pp'
require 'MeCab'
require 'kconv'
require 'bundler'
Bundler.require
 
def nihongo_to_roma(japanese, join_word=" ")
  m = MeCab::Tagger.new('-Ochasen')
  node =  m.parseToNode(japanese)

  elements = []
  while node
    item = node.feature.toutf8.split(",")[-2]
    pp item
    if item != "*"
      elements << item
    else 
      elements << Moji.zen_to_han(node.surface)
    end
    node = node.next
  end

  Moji.zen_to_han(elements.map(&:katakana_to_roman).join(join_word))
end

p japanese = "天二郎V2「CSSはかんたんです。よゆう！」"
p nihongo_to_roma(japanese)
#" ten ni rou V 2 ｢ CSS ha kan ta n desu ｡ yo yuu ! ｣ "