In a large bowl whisk together the wasabi paste, lime juice, sesame oil, rice wine, soy sauce, and hoisin sauce. Add sliced green onion, chili peppers, sesame seeds, cilantro (if desired), and mix well. Season to taste with sea salt and freshly ground black pepper. Set mixture aside for basting.
Cut tuna into large chunks weighing approximately 2 oz each (2 cubes). You will need 16 pieces.
Fill Cajun Injector with sake. Insert Cajun injector into center of one piece of tuna, and inject with sake. Repeat with all remaining pieces of tuna. Refill injector if necessary, and inject each shrimp with sake.
Thread 2 pieces of red onion onto fish hook. Add one piece of red pepper, followed by one piece of tuna. Add one piece of shrimp, piercing shrimp through head and tail, and finish with one more piece of tuna. Repeat with remaining 7 skewers.
Preheat grill to high.
Drizzle skewers with olive oil, and season with steak spice rubbing the seasoning into the fish. Place skewers onto grill. Grill skewers for 1-2 minutes per side, basting with sauce throughout the last half of grilling time, until shrimp are fully cooked throughout, and the tuna is medium rare.
Give skewers one final baste with sauce, and remove skewers from grill, and serve immediately with wedges of lime and wasabi.