Engage+ is probably my favorite lategame powerup in the series just for how drastic a powerboost it is as a purely combat enhancing Engage, and how it feels earned after one of the hardest chapters in the game
Turning Alear, who's probably a middling combat unit at this point in the game even if you made him a Wyvern, and his A Supports into demigods devastating the battlefield for 4 turns, and your partner still being able to use their own Ring immediately after, feels incredibly fun