Using this system is a great way to deal with boss fights or powerful base guards as you can activate Kizuna, perform attacks while the meter drains and right before it runs out, summon a duo attack which can take out hundreds of enemies at once. There is also the Kizuna system, which allows you to select between allies and perform attacks together. If you fill up your meter enough you can perform a more powerful attack that can wipe out an entire area.
The square and triangle buttons can be combined together to perform various combo attacks. Luckily for you, you possess almost godlike power and can easily dispatch enemies in front of you. You are dropped onto the middle of a huge battlefield with hundreds of enemies in sight. If you have played either of those, you know what you are getting into here. The gameplay remains mostly the same as previous One Piece games and Dynasty Warriors games.
Now, I haven't talked to any One Piece fans so I am not sure if they would enjoy this kind of story telling, but for people looking to get into the series, this is a great way to. Well, not every storyline but all of the major plot points and moments is represented here. As I mentioned before, the great part of this game is that even if you don't know anything about the series, this game can bring you up to speed as the main storyline spans almost the entire One Piece franchise from the manga to the animated series and the major storylines are represented.