Patti mostly speaks in a sing-song voice, acting and speaking like a little kid. She says "hullo" and "sowwy", like how a child says "hello" and "sorry". She is so naïve and simple-minded that she thinks everything is all fun and games and she does not take anything seriously, but many fanbases find this to be "cute" or "endearing." While taking an important written exam, instead of answering questions, she began making an origami giraffe out of her test papers, then "broke its friggin' neck". Her current personality differs from the seemingly aggressive personality she had during her time in Brooklyn, developing her current personality after she met Kid. Unlike her sister, Patti enjoys the drama brought on by Kid's perfectionist attitude, though she does cheer him up when he gets down on himself about it.
On the few occasions when she loses her temper, her childlike personality is replaced by a somewhat psychotic-seeming anger, as if her personality reverted back into her past street life in Brooklyn. There have been times though, that Patti's childishly naïve personality disappears to make room for a more serious personality, suggesting that her bubble-like personality may be a front, or merely how she wants to act. These changes are more evident in the manga, recent example of which was seen after Kid got 'collected' by Noah. Patti uncharacteristically called her sister a coward when she refused to fight Noah, and showed a surprising maturity by comforting her sister afterward.
Patty has chin-length, bright yellow (blonde) hair with bangs, light blue eyes and a larger breast size than her sister even though her sister is much older and taller than her. Both of the Thompson sisters wear cowgirl outfits: A tight, red, sleeveless, turtleneck belly shirt with a white tie, cowboy hat and black, high-heel boots. However, unlike Liz, Patty wears puffy shorts. There is also a subtle difference in her hat. Liz's hat has rims that slant forwards, whereas Patty's hat has rims that are in a perfect curve. Later on in the anime, both sisters wear white jackets over their outfits. Like Liz, Patty's soul has a pink color and has two curved triangles representing her hat. In Spartoi uniform, Patty wears a zip-up top over a blue vest and a jacket with a high collar like Liz. She keeps her puffy shorts but replaces her cowboy hat with a hat that has floppy 'ears' on each side.
Patty transforms into a boy upon entering the Book of Eibon. She is shown to have shorter hair covered by a beanie hat. She also resembles her psychotic self a bit more, as her eyes look slightly more crazed than in her girl form. She wears a white jacket and shirt and dark pants like Liz. The only difference is that Patty has the Spartoi logo on her left shoulder and a large Shinigami skull emblazoned on her back.
- It has been known that Patty got 2 points in the important written exam because of her giraffe in episode 14.
- Both Patty and Liz collect souls in the magazines of their gun forms.
- Patty seems to be ambidextrous, she uses her right hand to draw/write and shoots with her left hand.
- Her last name may come from the Thompson submachine gun.
- Her last name could also be a reference to the Thompson Twins pop group.
- In interviews Atsushi Ōkubo has mentioned that he feels Patty is the character most like him, mentioning Black☆Star also.
- In the official popularity poll taken by the manga's readers, Patty ranked 10th.
- Patty wears a pink thong.
- Despite her comical approach to test taking, the fact that Patti's Origami Giraffe with a broken neck still scored two points might say more about the tests at Shibusen than the students.
- In her male form during the Lust Chapter, Patti somewhat resembles Black Star when he is seen wearing a beanie after his second fight with Mifune. Likewise, Black Star's female form can be seen as remarkably similar to Patti.