You heard an explosion.
Walk to the right to meet Zoanoid. After your conversation you can walk further to the right. Walk past the palace and you’ll run into Tetsuro. Again a conversation and you can walk further. On the ground you’ll find a GUYVER BLOCK. Pick it up and walk further to the right.
When you want to continue your journey to the right you’ll meet Murakami. Follow this conversation as well to complete your quest.
Game source: A copy of the game was found here on the internet.