Main Menu

When you start the game, you will see the following message in Japanese:

"This game is free-to-play, but certain contents will require money to purchase."

After which the game intro will be played, which you can skip by pressing the left-bottom button.

After that, you will be greeted by the main menu.

Buttons
Top yellow button      = Game Start

Bottom yellow button = Option

g+ button                   = Google Plus Sign-In

Bottom-right button    = Presents for friends invitation

Game Start
This is where you can choose the chapters you want to play, or try to get a high score in Challenge Mode.

When you first start the game, you will only have Chapter 1. As you progress, more chapters and game features will be unlocked!

Check out the following links for more information:

Chapter 1

Chapter 2

Chapter 3

Legend Story

Challenge Mode

Option
You will see the options menu (see pic).

You can set music/sound to on or off here, log in to Facebook and see the official PONOS Facebook page.

As for the Japanese buttons:

Centre:

Top yellow button = Help. (Teaches you how to play the game! In Japanese.)

Middle yellow button = Opening. (You can view the Japanese intro again.)

Bottom small yellow button = Ending. (View the Japanese ending. Unlocked when you complete Chapter 1)

Bottom big yellow button = Staff Credits

Rightmost:

Top button = Change device (I have not dabbled in this yet, but basically you can sign in to Google Plus and port your Battle Cats data to another device. This will however wipe your data from your first device. Do a backup before you try anything.)

Bottom button = Push Notice On/Off

Presents For Friends Invitation
This feature is unlocked after you complete Stage 7 of Chapter 1.