Considering it has five past seasons of relationships and mythology to draw on, “Grimm” has been more focused on chugging ahead, even when that has meant dropping old plotlines and awkwardly reworking the characters’ motivations Given that context, it was a total pleasure to watch Friday’s “Blind Love,” the seventh episode in this sixth and final season. It gave the characters a chance to revel in a few nostalgic memories, as well the fun of seeing character pairing up in wacky new ways.