Hydrogen-rich superluminous supernovae (SLSNe-II), characterised by their extreme peak brightness (<-20 mag), represent the most luminosity end of Type II supernovae (SNe II). Their extreme brightness is thought to arise from a combination of massive progenitor, dense circumstellar medium (CSM), and the interaction between the supernvoa ejecta and CSM. However, the exact mechanism powering their light curve remains unclear. Additionally, their similarity to Type IIn supernovae (SNe IIn), which exhibit narrow interaction lines and are often slightly brighter than ordinary SNe II, has raised questions about the distinction between SLSNe-II and SNe IIn. In this study, we present an analysis of SN 2021aaev, a SLSN-II with well-sampled UV-optical photometry. Spectroscopic follow-up reveals flash ionisation features that persist for over 2 weeks, marking the first time such features have been observed in a SLSN-II. Flash features are common among SNe IIn and serve as strong evidence of CSM interaction. Given the rarity of studies on SLSNe-II with flash features, our work provides key insights into the powering mechanism of SLSNe-II and their distinction (or lack thereof) from SNe IIn