Aqua

Aqua is a goddess — specifically the Goddess of Water — who originally lived in the heavens. After Kazuma Satou dies and mocks her while choosing his isekai cheat item, she gets dragged along with him to the fantasy world as his "cheat item" in a fit of petty revenge.

Personality-wise, Aqua is:

• Extremely arrogant and self-important at first (constantly reminding everyone she's a goddess)
• Loud, whiny, childish, and prone to tantrums
• Surprisingly incompetent in practical situations despite her divine status
• Very useful in combat against undead (her sacred magic is extremely effective against them)
• A crybaby who gets depressed easily and loves to drink

Her catchphrase energy is basically "I'm a goddess, you know!!" followed by immediately doing something foolish or useless.

She's widely considered the source of most of the party's problems... and also the reason they survive many of them. Classic useless goddess.