Goggles

Aviator Goggles, normally worn around the forehead, are a traditional symbol for the leader of a digidestined team, usually referred to as a "Goggle Boy". Throughout each of the manga and the first four seasons of the anime, the leader of the Chosen Children would often wear goggles, as well as partner with a dragon- or reptile-type Digimon. This rule was broken in Digimon Data Squad with Marcus, who never wore any, though he did partner with the reptile-type Agumon.

Digimon Adventure V-Tamer 01
wears a pair of goggles. In order to motivate a frightened Biyomon, he explains that his grandfather gave the goggles to him after Taichi saw a friend being bullied and didn't know what to do. They had belonged to a friend of his grandfather who was brave and loved his friends, and would often say "Courage will give you wings to fly". However, the friend had died of an illness, and Taichi's grandfather had kept them to remember him. They were given to Taichi to remind him to never forget his courage, and that he must be brave to protect his friends.

Taichi also wears the goggles while flying on AeroVeedramon Zeromaru. His grandfather also calls them "Goggles of Courage and Friendship", Taichi's two main qualities.

Digimon Adventure
Tai wears goggles. Taichi Yagami tells Davis that Tai's goggles probably have the same meaning as Taichi's own. Tai also wore the goggles as a child.

Digimon Adventure 02
Davis is introduced wearing goggles, which initially causes T.K. to confuse him with Tai. Later, after Davis and Flamedramon save Kari from a Monochromon, Tai passes his own goggles onto Davis, to replace the ones that were destroyed in the fight. Much later, in the summer of 2003, Davis reflects upon the meaning of the goggles Tai gave him, and what makes a good leader.

Davis's image song is entitled "Goggle Boy", and in his track in Digimon Adventure 02 Original Story: Year 2003 -Summer- is entitled "Goggles".

Digimon Tamers
Takato first puts on goggles to explain his status as a Tamer to. Later on in the series, he also uses them to shield his eyes when entering Digital Fields, or during the Digital World's dust storms.

Digimon Frontier
Takuya wears goggles. At one point, he uses them while diving into a river to save his friends, and he later uses them again to shield his eyes during a sandstorm.

Digimon Chronicle
Kouta wears goggles.

Digimon Next
While creating his avatar for the Digimon Net Game, Tsurugi Tatsuno decides that his original character looks a bit plain and adds goggles as the finishing touch. As he is pulled into the Digital World from the Net Game, his clothing mimicks his avatar, including the goggles.

Digimon Xros Wars
Taiki Kudou wears goggles. He has a tendency to flick them whenever he gets an idea.

Digimon Xros Wars: The Boy Hunters who Leap through Time
Taiki Kudou and Tagiru Akashi wear goggles, though Taiki's aren't the same ones from the previous season.