Molecular phototheranostic dyes are of eminent interest for oncological diagnosis and imaging-guided phototherapy. However, it remains challenging to develop photosensitizers (PSs) that simultaneously integrate high-contrast photoacoustic imaging and efficient therapeutic capabilities. In this work, a supramolecular strategy is employed to construct a molecular pair phototheranostic agent via the direct self-assembly of two cyanines, C5TNa (anionic) and Cy-Et (cationic). The Coulombic interactions between C5TNa and Cy-Et facilitate the formation of a complementary cyanine pair (C5T-ET) and the creation of supramolecular CT-J-type aggregates in water. This complementary cyanine pair (C5T-ET) results in completely quenched fluorescence and significantly enhances nonradiative deactivation (≈22 ps), leading to a 3.3-fold increase in photothermal conversion efficiency and a 7.1-fold enhancement in photoacoustic response compared to indocyanine green (ICG). As a result, the J-type aggregate cyanine pair (C5T-ET) demonstrates high photoacoustic imaging capability and remarkable antitumor phototheranostic efficacy in vivo, highlighting its potential for clinical applications. This work provides strong experimental evidence for the superior performance of the complementary cyanine pair (C5T-ET) in enhancing photosensitization and photoacoustic response. It is believed that this strategy will propel the advancement of controllable dye J-aggregates and contribute to the practical implementation of photoacoustic imaging and phototherapy in vivo.