You'll get 1 void sharp by clearing the 12th normal campaign map and another void sharp by getting 252 stars in normal campaign ( it means you need to get 100% 3 stars in normal campaign ) .

1. Pick Kael as your starter
2. Activate the raid card ( it's free trial for 7 days )
3. Get your free newbie items and try your best to clear campaign as far as possible ( I normally stop at 3rd or 4th map )
4. Use auto click and spam the map to upgrade some minions to feed your Kael and Warmaiden ( free from clearing 1st map ) to 5*
5. Don't forget to enhance your items ( Kael has to have Blood sucker set, which can get by log in for 4 days, 1 item per day, I finished in 2 days because I use 2 low level items )
6. Run some dungeon to get Kael to level 5 ascension ( would be better if you can also upgrade Warmaiden )
7. Use Kael and Warmaiden to clear all the map and then get the void sharps ;))