Gantz

Successfully complete the game to unlock options at the "Extra Option" screen that allow you to select a new character, choose your weapons, partners, and battle items.

Beat the game with any character other then Kurono Kei. The Neko Mimi Alien mode will be found under the Extra Option Menu.

After beating the game once, go to extra option and select the first option. You'll get to choose a character to play as. You can also choose between weapons, battle items and partners.

Be kind with Kishimoto. Take here in your team as much as you can and act like a leader when talking to others. At the end of the game you'll be rewarded with Ending #4 featuring Kei and Kishimoto dating each other.

To play with the Gantz bike in story mode, you need to get a 100 points. Once you did that you will be returned to the Gantz Room. There will be a screen with 3 choices. Choose the one in the center and you'll be rewarded with the Gantz Bike. Load the clear save file you obtained and the Gantz Bike will appear in the accessories at the begining of a mission.