A simultaneous living anionic copolymerization of a concentrated solution of deuterated styrene (S) and nondeuterated isoprene (I) monomers in deuterated benzene as a solvent was studied by a combination of time-resolved measurements of small-angle neutron scattering (SANS), size exclusion chromatography (SEC), nuclear magnetic resonance (NMR), and ultraviolet-visible spectroscopy (UV-vis). The molecular building-tip process and its consequence on the bottom-up self-assembling process during the copolymerization reaction were observed on three different length scales on the same batch of the solution, which enabled us to explore simultaneously the time changes in the local structure (living chain ends), the primary structure (propagating chains), and the higher order structure (microdomains). We found that the copolymerization process was divided into two time regions, defined by regions land II. In region 1, the copolymerization of Sand I monomers took place, and all I monomers were consumed at the end of region I. In the early stage of region I (region I-a), the SANS profiles were almost time-independent and exhibited no scattering maximum, whereas in the late stage of region I (region I-b), a scattering maximum appeared at q(m) and hardly changed with time, although the maximum intensity I, slightly increased with time. In region 11, pure polystyrene (PS) block chains were formed. (1,11 and 1,,, rapidly decreased and increased, respectively, and the polymerization-induced disorder-order transition (ODT) and order-order transition (OOT) were observed. The living polymers having isoprenyl anion at the chain end (denoted hereafter by PI) started to change into those having styryl anion at the chain end (denoted hereafter by PS), and hence the polymerization of S monomers occurred under the coexistence of PI- and PS-. As a consequence, we found an increase in the polydispersity index of the molecular weight, M-w/M-n, and a slower effective reaction rate of S monomers relative to the corresponding homopolymerization of S monomers.