The Action Role Playing Game (oh, so that's what ARPG stands for) is a free to play browser based game that "combines the role-playing, real time battle of ARPG with the "tower defense" battle mode", as peculiar a team-up since Ric Flair and Roddy Piper in 2006. Tower defense games - while highly enjoyable - are not known for their back and forth action elements.
But, the game is promising a new gameplay experience and I cannot argue with this combination. It's certainly new.

OnePiece Online close beta test time: Jan 15 2015@ 00:01 –Jan 21 2015 @ 23:59
OnePiece Online offical site:http://www.joygames.me

The game consists of 300 separate instances that players must manage with a good deal of strategy, battle acumen and a fair amount of luck. Choose your characters - from the hundreds found throughout the long running One Piece universe - and set sail to glory and riches. Want Luffy and The Yonko to team up? Go right ahead. The combinations are endless.
The beta will last for seven days, and is designed "for technique testing purposes, so emergency maintenance or system data rollback may occur during the beta period." At the end of the seven day period, all character data will be erased. Participants will be rewarded for their patience and enjoyment with various in-game items and points, which you can read about here.

Head over to the official One Piece Online site to sign up today.