Main Characters seen in different media from top to bottom are Yōji Itami, Lelei La Lalena, Rory Mercury, Tuka Luna Marceau, Yao Haa Dushi, and Piña Co Lada; source, redditmedia.com
The Main Characters in GATE are Yōji Itami, Lelei La Lalena, Rory Mercury, Tuka Luna Marceau, Yao Haa Dushi, and Piña Co Lada.
Gallery
This art contains the Main Characters per volume of the Manga. Take note that not all of the volumes are available.
Main Characters Manga volume 1.
Main Chracters Manga volume 3.
Main Characters Manga volume 4.
Main Characters Manga volume 5. Note Pina is on the main Character page with Itami and the others.
Main Characters volume 6