A Trinity Bonus is achieved when you attain the No Damage Received Bonus, Genocide Bonus (kill all enemies), and the bonus you get for completing a mission that is a higher level than you. To get this easily, start off Raid Mode by doing mission 2 (Beach) which is a lvl 2 mission, and you should be level 1. Kill all of the enemies, be sure to get the blowfish enemy in the water to the left of the starting area, and make sure you don't get hit. If you don't do it your first try, head to the character screen in the Raid Menus and use to set your lvl back to 1. You can change your level later, but this will allow you to get the level bonus, while keeping your from using weapons above level 1.