Relativistic jets are thought to play a crucial role in the co-evolution of massive galaxies and their central supermassive black holes (SMBHs). Yet, our understanding of powerful radio sources during or near the epoch of reionization remains limited—posing a significant gap, particularly for future studies aiming to detect 21 cm absorptions (i.e. to study the properties of the Intergalactic Medium) in this early cosmic era. In this talk, I will present the discovery of the most distant radio-loud quasar known to date at z = 7.0 – a blazar, whose relativistic jets are pointed toward Earth. This system represents an extreme case of highly accreting SMBH in the early Universe, requiring accretion rates near the Eddington limit to power both its luminous accretion disk and relativistic jets simultaneously. The existence of this blazar implies a population of hundreds of similar, misaligned highly accreting radio sources at z?7, suggesting that jet-mode feedback was already established in the early Universe. I will highlight our ongoing efforts to characterize the properties of its powerful relativistic jet across the electromagnetic spectrum, from low-frequency radio observations to X-rays. Finally, I will discuss the potential of this source as a background beacon for 21 cm absorption studies, drawing on new data from my uGMRT and LOFAR observing programs.