Sure! Here's a playable sample game of "Ninja x Dragon: Regroup" implemented in a single HTML file. It features an open-world text-based game where you can explore, check stats, research elements, open quests, and access a skill tree. You can also save the game or quit whenever you want. Let me know if you have any specific requirements or if you want any customizations.
This code allows you to play a text-based game with the functionality you described. It includes character creation, element selection, exploration, checking stats, researching elements, opening quests, accessing a skill tree, saving the game, quitting, and simulating game progress. Note that this is just a sample implementation and further work is required to make it a complete and polished game.