As part of his nefarious plan, Naraku tricked Sango into attacking Inuyasha, and gave her a Sacred Jewel shard to prevent her from feeling pain.
Sango soon located and attacked Inuyasha, but he was able to convince her that Naraku was lying.
He explained that the one who killed them was the hanyō Inuyasha.
Sango overheard this conversation, and declared that she would kill Inuyasha for murdering her family and friends.
Sango, unfamiliar to romance, reacted shyly to his advances.