Photochromic materials with rapid response and high stability are essential for progressive anti-counterfeiting and secure information encryption technologies. Herein, we report a Förster resonance energy transfer (FRET)-assisted strategy to boost the photochromic properties of high-crystalline C3N5 nanosheets (HC-C3N5) by integrating carbon dots (CDs). The incorporation of CDs significantly increased light absorption, fluorescence intensity, and energy transfer efficiency, leading to an ultrafast and reversible color transition from dark yellow to green under UV irradiation, with complete recovery within 180 s and excellent cycling stability. Transient photovoltage technique (TPV) test confirms a non-radiative energy transfer pathway between CDs and HC-C3N5, excluding the possibility of electron transfer. Building on the distinct photo response characteristics of bulk C3N5 (B-C3N5), HC-C3N5, and CDs/HC-C3N5, this study further explores their potential in multi-layered anti-counterfeiting labels and a time-resolved encryption system, enabling dynamic optical information encoding. This work not only reveals the key role of the FRET mechanism over CDs in modified photochromic materials, but also pave the way for next-generation anti-counterfeiting and secure data storage applications.