What are the limits of nuclear existence? How do the limits of weak binding and extreme proton-to-neutron asymmetries affect nuclear properties? These are two of the key questions raised in US2002 Long-Range Plan for Nuclear Science. Now that we have the first of new-generation RI-Beam facilities, the RI Beam Factory (RIBF) at RIKEN, Japan, we may take a quantum leap towards the limits of nuclear existence on the neutron-rich side: the neutron drip line, whose experimental study we have long been limited to only light nuclei below 
oxygen isotopes. 
In this seminar, after introducing briefly this new facility, I will 
present new results on breakup experiments on weakly bound drip-line nuclei in C and Ne isotopes at the relativistic energies of RIBF[1]. 
The main focus is on how we can investigate exotic structures, such as halo structure, by Coulomb breakup on heavy targets and nuclear breakup on light targets. Halo structures, where the wave functions of one or two valence 
neutrons extend beyond the range of the nuclear interaction due to quantum tunneling effect, have been found near the drip line but only in the light region below A<20. 
In the new experiments at RIBF, we have indeed found experimental evidence that 22C and 31Ne are both halo nuclei. Implications of these findings, more and near future plans using breakup reactions at RIBF will also be discussed.