The game is fun, but I think the game could use a little more insentive for friend collecting.
You essentially create a team of 3 friends to be a defending team and another 3 to be an offensive team.
Every week up to 5 times you get to challenge a random player's defending team with your offense team and if you beat them, you are rewarded with points to move up a tier and fight other players defensive teams who are also higher tier.
(Another thing that Crossing Void has is earning more points if you use a specific unit, you can implement that factor here too as there are a lot of friends who go unused due to the sheer amount of them.)
At the end of a season (say a month) the higher tier you are, the more you are rewarded. This is a good way to earn seal crystals, paper dolls and fortune dust (or whatever other rewards you deem fit)
This here would also give more insentive for the gacha whales who spend all their money on the game for the best units, theres not really much use for the strongest friends if you cant show them off.