1. Fruit Pastilles = suitcase?
Yes, you can put as much stuff as you like into your suit case from Birmingham. Just notice that you will not see it again until you land in Tokyo. But always good to bring with you some familiar sweets, though the Japanese have similar good stuff locally also.
2. Do I need to declare them? If so how??
No.
3. I'm going from Birmingham- Copenhagen- Narita...
Great route, easy peasy! No worries really, all well coordinated and developed 'western world style' all the way for you.
(Disclosure, I am Danish myself but living abroad since 1991)
4. at Copenhagen how will it work?
You land from UK, so you will already be in the INTL flight departures area.
Cant say though if you need to walk from one gate area finger to another, as depend on their flight arrangements.
But it will in any case be a short walk of 10-15 mins max in roughly the same terminal area.
(max in from the finger you landed in, up to the main intl airport main hall and then down out in the gate finger your plane to Tokyo departs from)
5. Will I see my suitcase?
No. You check it in direct to destination when dropping it in Birmingham.
6. Will I need to declare medical hand held stuff again?
No, most probably not. Actually as it is, I never ever declared any medical handheld ever in my life and I fly non-stop. But yes, you might need to go through a body and handheld luggage scan again to get out to your Tokyo departure gate.
As it is, they spend more time security checking you hair-gel and toothpaste tubes these days.
7. Will I need to declare Fruit Pastilles again?
No, and you never needed to in the first place.
8. at Narita will I need to declare medical equipment & fruit Pastilles or none?
None. Its not fresh farmer produce, its not vegetable seeds, its not a live organism. Its not illegal drugs, its not...
Btw, I always buy one or two 1/2liter bottle of full sugar drinks to take in my hand luggage, when landing in the last transit airport before getting onto one of the long-haul flights to the Americas or Asia, as you then always have that handy with you both in the airplane but also when you land in your destination airport 12-20 hours later. And as you are in the already security-checked zone, then you are allowed to bring that onto the airplane in your hand luggage. And this is great as especially when landing in that foreign place, you don't know always how quick you can proceed through immigration and passport controls, how far you need to walk and to get your checked-in suitcase etc before you can get outside into the arrival hall where you have shops and ATM machines to be able to buy your sugars locally in case you should go hypo in all the excitement.
Enjoy and have a great trip - Yōkoso!