Well, I found the below unlock conditions a while ago:
- Extra: The usual.
Now has a video, by the way.- Miracle: Extra + 60 spells. Look familiar?
- 4th playable team for main game: Clear Miracle with all teams.
As for the last words, they're all listed ingame. I was in the process of entering them all on the spell card page but never finished:
135 (Index): Cap all St1 cards, any difficulty, any character
136 (Nue): Cap 14 (Nue's Lunatic card), any character
137 (Mamizou): Cap all St2 cards, any difficulty, any character
138 (Iku): Cap 28
139 (Misaka Sisters): Cap all St3 cards, any difficulty, any character
140 (Yuyuko): Cap all St4 cards
141 (Ran): Cap 60
142 (Yukari): Cap all St5 cards
143 (Motoharu): Cap 80
144 (Aleister): Cap all St6 cards
145 (Last Order): Cap 38, 112, 123
146 (Accelerator): Cap 113-122
147 (Teitoku): Cap 125-134
148 (Reimu): 1cc Normal with Marisa/Mikoto
149 (Marisa): 1cc Easy with Sanae/Ruiko
150 (Sakuya): View a parallel ending (conditions same as TD)
151 (Sanae): 1cc Extra with Sanae/Ruiko
152 (Touma): Cap 148
153 (Mikoto): 1cc Normal with Reimu/Touma
154 (Kuroko): 1cc Hard with Sakuya/Kuroko
155 (Ruiko): 1cc Miracle with all characters
The difficulty isn't nearly as bad as Len'en, but some cards are indeed annoying (Yuyuko's 1st, to a lesser extent Yukari's survival).