This paper presents the first non-interactive, succinct, and secure representation of a PoW-based blockchain that operates under variable mining difficulty while satisfying both completeness and onlineness properties. Completeness ensures that provers can update an existing NIPoPoW by incorporating a newly mined block, whereas onlineness ensures that miners can extend the chain directly from a NIPoPoW. The time complexity for both the prover (to update a NIPoPoW with a new block) and the verifier is logarithmic in the number of blocks of the underlying PoW blockchain. The communication complexity required for synchronization is polylogarithmic in the length of the blockchain. We prove the correctness of our scheme in the presence of a 1/3-bounded PPT adversary.