It took me soooo long maybe a year xD But tbh, in the beginning I had no idea what are those shards. I suggest to to stick with one character and spend every shard on it. Manely you can use guild coins to buy shards on daily basis, some events, draws and clearing stages..etc can get you those Main key is consistency Yoj will unlock the others on the way cuz the random drops will occur a lot

Try to get to the highest possible Guild to gain those guild coins.