The overdive system in The 3rd Birthday does more than let Aya switch locations. When you swap mind and body with an ally on the battlefield you get to use their weapons.
After Aya tests out a gun she can buy it by spending BP (battle points). Aya gets to keep the guns players equip before a mission starts even when she dives into another character. You can further customize guns inside the Weapon Bank with parts to raise their stats. Guns in The 3rd Birthday have five parameters: weapon power, bullet power, bullet impact, handling, and range. Aya also has five weapon proficiencies: handgun, assault, shotgun, sniper, and launcher.
As a finishing move, Aya can also kill the Twisted by diving into them. This move, called an Overdive Kill, nets Aya DNA chips. Players can fix and fuse these chips on her Over Energy board to gain access to new abilities.
The cross healing ability, for example, adds a fixed chance that Aya will recover some life when she triggers a crossfire attack.