If you recruited Lysithea before the timeskip she automatically joins you already on BE. But if you didn't recruit her, you still have the option again when you defeat her in battle.
Why wouldn't you recruit best mage?
Originally Posted by Deathhappens
Really, all 3 of the romances in F/SN are 'for want of a nail' kind of situations.
Originally Posted by forumghost
You mean because Shirou winds up falling for the first of the three that he Nailed?
Originally Posted by Tobias
I speak for the majority of important people* *a category comprised entirely of myself