Siren (video game)/Headscratchers

Something about the sound of the Siren itself bugs me. Word of God is that, in the original game, it's the scream of Datatsushi. However, in the bonus cutscene, you can quite clearly hear Datatsushi's scream and the Siren song at the same time, and they're very obviously different sounds. So... how does that work?
- The one where they're noshing on him? In that particular case, the Siren may have been for dramatic effect, although since D's an extradimensional alien, it's possible that his voice has some unusual properties.
So why did Tamon go to Hanuda? The guide says it's his hometown, but then why'd he bring Yoriko, who he doesn't seem fond of anyway? And who the hell is Akira? What's he doing there? Is he a native, or just some elderly hunter in the wrong place at the wrong time?
- Hanuda is where Tamon was born and grew up until he lost his parents in an earthquake/landslide in 1976, when a failed attempt to summon Datatsushi caused Hanuda to be drawn briefly into the Netherworld. When he grew up, he became a folklorist, who returned to the area to do research on the local religion. Yoriko seems to have invited herself along against Tamon's will. Akira is a native, or at the very least someone who moved into Hanuda prior to 1976 (when he lost his wife in the same incident that killed Tamon's parents), and doesn't appear to have subscribed to the local religion.
If Hisako wanted to summon Datatsushi, why has she been carrying out the rituals for all these years? I thought the ritual was used to placate it and prevent it dragging the village to another dimension. Did she only decide to summon him after everything went to hell (literaly)? Am I missing something here?
- The ritual is to revive Datatsushi by appeasing it. Hisako "ate the fruit", so she has to "give it back" in the form of her descendants every once in a while. Miyako was going to be the last one needed.