Originally Posted by
Taon
Fastest?
That's easy enough: spend money to buy FGs, roll gacha, sell/merge girls.
Wouldn't recommend it myself, but that's the fastest way right now.
If you want the fastest without spending any money, then Drip and Hypo have you covered; though I should point out that Hypo's way is probably faster if you don't have a ton of gacha seeds. 3* units only give 10 bond crystals, 4* 100 but getting a 4* on the normal gacha is about as likely as getting a 6* on the premium gacha.
This begs the question though; why do you need bond crystals ASAP? The only thing you can buy with them are the second affection items, and those can be acquired with Sun Medals from whaleship as well. If you can't manage any whaleship missions, then I would suggest that worrying about second affection right now is putting the cart before the horse.