The story is fairly straight forward compared to stuff like the console games (better than Sacred Stones at least), but the real meat of the game's writing is in the supports.
What exactly is the spotpass thing?
When I get this game, I want to make sure I don't miss anything due to all these newfangled concepts. O_O
It's where you get the free DLC and other WiFi based benefits.
Streetpass is the other wireless 3DS function and is what you use to beam avatars from other players as well as beaming your own avatar elsewhere.
If you've ever played DQIX, the SpotPass function would be analogous to the online shop and post game quests; whereas the trading maps, unlocking improvements to the Inn, and the feature that only really works in Japan or conventions are analogous to the 3DS's Streetpass.
From Blazing Sword, I've only seen Lyn so far. I saw Caeda from the Altea games, Eirika from Sacred Stones, Lilina from Sword of Seals, Alm and Celica from I think Holy War & Thracia 776 and..... others. Oh yeah. Ike and Elinica from the Radiant games. I think there was more but I forget who.
Lyn, Florina, Nino, Serra, Eliwood, Hector, Karel, Matthew, Jaffar, and Nergal are this round's SpotPass units. The others will show up later but you can get a sneak peak through the DLC missions (with the initial one for paid DLC Marth being set on Telys Island and involving a
showdown between the leading ladies of the earlier games versus Marth, Ike, Alm, and your guys).
(Also, Alm and Celica are both from Gaiden, either Diadora, Julia/Yuria, or both are from Holy War, and most likely Mareeta, if anybody, is repping 776 in that mission.)