The trilogy includes a variety of species to populate the Milky Way Galaxy, and each has its own history, culture, and defining features. While there's a lot to explore when it comes to the races of the Milky Way, details that pop up early in the trilogy can lead to questions that are answered later or perhaps only answered through digging into extra information provided either in the game or through additional content. Questions like why Tali and the rest of the Quarians wear special suits are luckily answered through completing quests.
Quarians are one of several races that call the Milky Way their home, and Tali represents them in the trilogy sinceshe's the only Quarian who joins Shepard on the Normandy. Additionally, she can be recruited in all three games, giving Shepard plenty of time to learn about her and the Quarians. As it turns out, Quarians and Geth have a complex history with each other, and that factors into the reason Quarians wear their suits.
Understanding the importance of Rannoch to Tali and the rest of the Quarians first requiresunderstanding how they ended up creating the Migrant Fleet and living there rather than on their homeworld. This also ties into why Quarians and Geth are enemies in since the conflict between these two led to the Quarians evacuating Rannoch. When the Geth showed signs of becoming sentient, the Quarians planned to eliminate them.
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This plan backfired, and the Geth wiped out most of the population, leading the remaining Quarians to flee the planet. With living on their home planet no longer an option, the Quarians developed the Migrant Fleet, also known as the Flotilla, as their new home. Naturally, this had cultural impacts that led to Quarians needing to wear special suits to survive, using technology to live on overcrowded ships, and having the young people go on pilgrimages to
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