Seilin is the older sister of Julin and Kalin. Her name means "holy bell" ("sei" translates to "holy" and "lin" means "bell"). When Fuun San Shimai LIN3 begins, she is at least twenty years old. She is an infamous pirate queen, known for being fearsome.

Physically, Seilin has dark blue eyes and long, dark blue hair that falls past her shoulders. A section of the left part of her bangs is tied to the side and is dyed green (though in some images, it's colored orange or red). She does not physically resemble her sisters, as they all have different mothers. She wears a black bodysuit, tight blue shorts, and black boots. Sometimes she will also wear a long coat. Around her waist are ropes, to which she ties her bell.

Seilin is an extremely strong fighter; she even has the ability to walk on air and fly. She is not, however, a member of any martial arts clan, as she grew up with and was trained by pirates. As for her personality, she tends to be cold and aloof, but she also has a quick temper and sometimes acts impulsively. Despite her rough, usually rude nature, she occasionally demonstrates kindness to Julin and Kalin.

Like her sisters, Seilin has a pet animal. Seilin's pet is a swordfish, whom she can ride. The English adaptation calls the swordfish both "Sabre" and "Sword." In the Japanese manga, Seilin and Shark call the swordfish "Kaji," which is short for "kajiki," the Japanese word for "swordfish."

Seilin's bell has a fish tail/fin engraved on it. She received it when she was ten-years-old from her mother.

Shark's nickname for Seilin is "Sei." In the original Japanese manga, Shark's name is "Shaayuu", which is a transliteration of "shark." Seilin calls him both "Shaayuu" and the nickname "Shaa." Seilin's sisters eventually call her "Seilin-san."