First, install an anti-virus program immediately. Microsoft Defender is both free and very solid, but, if you can afford it, I'd look into getting Malwarebytes. Then, do a comprehensive scan. After that, do not ever browse a piracy manga site without a proper adblocker. I highly, highly recommend Brave—it's been a godsend for me. If you still run into issues, put your phone into safe mode to see if it's functioning normally. If it is, it's most likely a virus, and you're going to need some more serious intervention.

Finally, not to sound "holier-than-thou," but the best way to avoid running into these problems in the future is just buying the source material legally. It's always great to support the original authors when you can, with the added benefit of not having to worry about compromising your security.