There are also a few other things going on with Erica
Oh Tatsuya loves his sister but purely as a sister and only a sister. If someone hurts her he will destroy them, but I doubt he would block any romantic relationship she would want to go after baring one with him.
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Higurashi: Its a bit like watching a trainwreck, except you keep getting to see different trains wrecking with roughly the same passengers, into a variety of different objects. Also, the trains are driven by monkeys. On LSD.