Something very strange from Fire Force, season 1 episode 7, Hibana says "I swear in the name of St. John's Wort and the malice it represents." (Subbed) This must be a mistranslation. I don't see how St. John's Wort, a herbal remedy used in traditional medicine all around the globe, could represent malice. She must have been referring to some sort of poisonous herb, like hemlock, and the translators must have mistranslated the name.

[Update] Took forever, but there's a japanese horror film called "St John's Wort" and apparently:

"The title refers to a field of St. John's Wort planted in front of the house, which a character makes sure to point out means "revenge" in flower language." [1]

And this: "In hanakotoba (花言葉), the Japanese language of flowers, the St. John’s wort (弟切草) represents “superstition” (迷信), “animosity” (敵意), “secrets” (秘密), and “resentment” (恨み). [2]

And finally, I discovered the Japanese language of flowers:

1. The camellia is an early spring flower native to Japan. Among warriors and samurai, the red camellia symbolized a noble death.

2. Chrysanthemums have noble connotations, appearing on the Japanese Imperial Family’s crest for generations. But white chrysanthemums indicate purity, grief, and truth, and are used for funerals.

3. Wisteria or fuji are purple flowers which grow on woody, trailing vines. They’re a popular spring motif, especially for traditional fashions such as kanzashi and kimono. In the past, wisteria was associated with nobility as commoners were forbidden from wearing the color purple.

[1] https ://www.lovehkfilm.com/panasia/st_johns_wort.htm

[2] https://kyorinrinswritingdump.wordpress.com/2022/01/06/st-johns-wort-「弟切草」/

[3] https://theculturetrip.com/asia/japan/articles/hanakotoba-the-secret-meanings-behind-9-flowers-in-japan/