Unfortunately there's only so much special meals JAL could offer. There's a minimal allergen meal option but I am not sure if seafood is included as ingredients. Your safest bet might be to order a vegetarian dish and try to avoid Japanese dishes as they usually contain some kind of seafood.

But it is always a good idea to have your allergy medication with you at all time especially when you fly. Although airlines will try its best effort to offer the special meal you ordered, the food might still get traces of allergens from the kitchen prepared the meal or even the galley onboard. So definitely have the medications ready even if you order the veggie meals.