In order to introduce a new promising material for hydrogen storage application, Nickel (Ni) has been decorated on C12N12 nano-cluster. Firstly, the binding mode of Ni on C12N12 could be thought to be a bridge in between C, N (denoted as C-(μ-Ni)-N) or C, C (denoted as C-(μ-Ni)-C) or N, N (denoted as N-(μ-Ni)-N) resulting in three distinct geometries (abbreviated as XCN, XCC, and XNN isomers, respectively). Owing to the variation in the bridging mode of Ni, the interacting properties with the hydrogen molecule are expected to be different. The spontaneity of formation of Ni-C12N12 and 4Ni-C12N12 in terms of ΔHºf of isodesmic reactions indicate the possibility of getting promising high-energy-density materials (HEDMs). Further, we have investigated whether Ni, being a 3d transition metal, can influence the aromatic behavior of C12N12 nano-cluster. The binding energies and natural bond orbital (NBO) charges have been computed and energy decomposition analysis is carried out for Ni-C12N12 isomers. Decoration of Ni on XCN isomer releases slightly lower energy (~107.4 kcal/mol versus ~58.6 kcal/mol for XNN and XCN respectively). The hydrogen adsorption capacity of the strongest and the weakest Ni-bonded Ni-C12N12 nano-clusters (XNN and XCN isomers, respectively) has also been investigated.