A red card (赤札,red card) or (赤いカード,), also referred to as a slip or notice, is the F4's "declaration of war." The F4 gave red slips to those who defied or crossed them, such as Kimoto and Tsukushi Makino. Occasionally, Tsukasa Domyoji would give a notice without asking the other F4 members.
One of the F4's victims during their high school years was Kimoto, who stood up to them by saying "who care's about hte F4?!" Despite being popular prior to the incident, Kimoto was presumably bullied until he transferred schools.
Tsukushi Makino received a red card after defending her friend Makiko Endo, when the latter fell down a flight of stairs and landed on Tsukasa Domyoji. Instead of Makiko, Tsukushi was given the card after calling Tsukasa a "pea-frog" and further insulting him. Tsukushi delivered her own notices to the F4, saying "this is my declaration of war!" Afterwards, the other students began bullying Tsukushi, such as throwing eggs at her and stealing her desk. She overcame these tricks easily. Tsukushi continued to be bullied by her peers, but less frequently.
After seeing Tsukushi and Kazuya Aoike happily talk, Tsukasa issued a red slip to Kazuya. He was confronted by Tsukushi for his actions. Their fight escalated quickly until Tsukasa slapped Tsukushi, which she answered with a punch. Kazuya was bullied in similar ways as Tsukushi before him, though somewhat more harshly. Tsukushi stepped in to help him, when someone used a plunger on his face. They ran eventually ran into Eitoku University's cafeteria, where they were saved by Rui Hanazawa.
The red card appears in Meteor Garden, bearing the words "You'll be dead - F4". Like the manga, Ah Shu (Kimoto) finds his in his locker, however Shan Cai's (Tsukushi) is placed on her back. Shan Cai fashions a new red card, bearing a skull and crossbones, and sticks it on Dao Ming Si's (Tsukasa) head.Chen Qing He, Shan Cai's friend, received a card, after Si became jealous of their friendship. Another red card appears in Shan Cai's locker, but it was later revealed to be apart of Xiao Shun's plan.