How it is possible to create coins only with the proof of stake system?
The problem you are describing is: how do you mine coins in proof of stake if you have no stake? In essence; you can't, depending on the implementation obviously. If you don't have any coins, you won't be able to mine new blocks. The easiest solution is obviously buying coins from another. If the original creator(s) of a PoS coin simply sell most of their early work, others could start mining as early as the third block (genesis block to finance the creator, second block to transact to others).