The more gems you have better access to all those nifty gadgets, upgrades and secret agents you'll get. You can alwyas purchase gems in apps store. Prices are:
2,500 Gems ($0.99)
7,500 Gems ($1.99)
25,000 Gems ($4.99)
75,000 Gems ($9.99)
200,000 Gems ($19.99)
The sequel to the award winning Hellblade: Senua’s Sacrifice, Senua returns in a brutal journey of survival through the myth and torment of Viking Iceland. Intent on saving those who have fallen victim to the horrors of tyranny, Senua faces a battle of overcoming the darkness within and without.