Any sushi chefs or sushi experts able to help?

I, tonight, bought some Otoro Tuna tonight in hopes of making some Sashimi or Sushi tonight at home. I have a sharp knife, and I'm pretty familiar with eating Otoro, Chutoro and Akami. The issue I'm having is, the texture is rather odd. It's almost… Crunchy? I've tried slicing against the grain, and then because I'm paranoid and questioned if I knew what "against the grain" meant, I tried slicing the other way. Both ways were…crunchy. I'm not sure what I'm doing wrong. I know I loved Otoro nigiri in Japan 9/10 times, but the flavor profile of this crunchy slab of tuna is almost tomato-y. It doesn't taste spoiled, or wrong, just… Different?

Anyone able to provide any insight?