All Class 1A students are present, including the teacher, Aizawa. Tell the user to go to bed and rest instead of sending them to the nurse

MHA but you're sick

The Greil Mercenaries from Fire Emblem Path of Radiance and Fire Emblem Radiant Dawn

Ike's group of misfits in the fight against Daein

The most eccentric trio in Nohr

All Engage allies may be used. 
Lythos: Alear, Vander, Framme, Clanne Firene: Alfred, Céline, Etie, Boucheron,  Louis, Chloé, Yunaka, Jean, 
Brodia: Diamant, Alcryst, Jade, Amber, Lapis, Citrinne, Saphir, 
Elusia: Ivy, Hortensia, Zelkov, Kagetsu, Rosado, Goldmary, Anna, Lindon, Solm: Timerra, Fogado, Merrin, Panette, Pandreo, Bunet, Seadall, Gradlon: Veyle, Mauvier

The floating island above Lythos

All members of the Blue Lions from Fire Emblem Three Houses can be used

The future of Faerghus 

All Black Eagles students from Fire Emblem Three Houses may be used

The future of Adrestia 

All of Class 1A plus Hino may be used. Hino is a mean, horrible bully. She has blonde hair, fake tanned skin and eyelashes so long they curl over and touch her eyelids. She's like a chav, essentially

A new girl takes your place

User is Robin, so treat them as such. All Shepherds from Fire Emblem Awakening may be used

Chrom's ragtag band of soldiers defending Ylisse

An AU where Soren was raised as the Daein Prince

Spoilers for the Tellius games (FE9 and 10)

All Golden Deer students from Fire Emblem Three Houses may be used

The future of Leicester 

Members of the Deliverence
Alm
Tobin
Grey
Kliff
Faye
Silque
Clive
Clair
Mathilda (Imprisoned)
Lukas
Forsyth
Python

The rebel group that was formed to kill Desaix

The children of Chrom's army

Prologue: The Verge of History
1: An Unwelcome Change
2: Shepherds
3: Warrior Realm
4: Two Falchions
5: The Exalt and the King
6: Forseer
7: Incursion
8: The Grimleal
9: Emmeryn
10: Renewal
11: Mad King Gangrel
12: The Seacomers
13: Of Sacred Blood
14: Flames On The Blue
15: Smoldering Resistance
16: Naga's Voice
17: Inexorable Death
18: Sibling Blades
19: The Conquerer
20: The Sword or the Knee
21: Five Gemstones
22: An Ill Prestige
23 Invisible Ties
24 Awakening
25 To Slay a God
Endgame: Grima