I see that my friend @RatioTile already gave the critical information about this trip. He and I went on this 40 days trip together in November-December 2022. Both of us target to see the rarest of species in the country as well, so I believe we can help you with your trip. I'll follow your itinerary with the information that could be useful:
1) Kobe Animal Kingdom/Kobe Oji Zoo: Easily combinable, easy to see most of the rarities as well. The shoebill enclosure is exquisite. The striped possum pair is always sleeping, but their little house is turned towards the window so you will see them for sure. If you wish to see them active, the zookeepers are very helpful at Kobe Animal Kingdom so I just recommend asking for assistance. The Tibetan blue bear at Kobe Oji Zoo goes inside an hour before closing time. Go to his enclosure first when you arrive, you should have more than time enough.
2) Atoa/Suma Aqualife Park Kobe: We haven't been to Atoa ourselves on our trip. I briefly looked into it but I'm unsure if there is anything rare at this place. Suma Aqualife Park Kobe is under construction. Only half the aquarium is open for visitors and the rare species are mostly gone or off show. The sea snake collection is moved to an aquarium overseas. If you ask me, skip both these aquariums and choose a better option.
3) Osaka Aquarium: Amazing aquarium. You will love it. Target the New Zealand tank, there are some very rare fish species there like Meuschenia freycineti & Parapercis colias. In the main tank I'm guessing the whale shark is of importance to you, but also don't forget the sharpnose stingray. They have many. The arctic species are also one-of-a-kind.
4) Tennoji Zoo: We haven't been here either, because there are barely any species that are mind-blowing. I would try to combine this with the Osaka Aquarium as well, especially since the latter is open until 20:00 in the evening. Don't waste a day at Tennoji Zoo.
5) Toba Aquarium: Another amazing aquarium. Seeing the commerson's dolphins, African manatee, dugong & finless porpoise is very easy. You can't miss them. The fish collection itself is rather disappointing. They do have a few rare morays and mandarin dogfish on show. They also have an Amphiglossus reticulatus, but he is always sleeping. You probably still see it in that position though. I'm not sure if there is any way of reaching ISE Sea Paradise without a car, but if you manage to find a way than this place is perfect to combine with Toba Aquarium. It is tiny but has a lovely sea horse collection & they got two African clawless otters.
6) Atagawa Tropical and Alligator Garden/IZoo: These places are a real pain to get to. It's obviously your own decision if the travel time and costs are worth it, but if they are, then I sure recommend both locations. Atagawa's Amazon manatee is very easy to photograph, mainly because his enclosure is horribly small. The park also got a couple uncommon crocodile species like New Guinea crocodile. IZoo's Galapagos land iguanas are on show. You can see multiple adults and babies throughout the park. They also have Fiji crested iguanas, which are very rare in Europe. Other interesting species include Exuma Island iguana, Bahamian rock iguana (C. rileyi rileyi) & Galápagos lava lizard.
7) Zoorasia: Great park. Really beautiful. Proboscis monkeys are not on show during the winter period, only when it is warm enough outside. Crested argus & goliath imperial pigeon are easy to see, the first isn't as easy to photograph though. Tibetan macaque is only one animal left but she is active. Also give some attention to the woolly monkeys, which are believed to be a different (sub)species than we have in Europe.
8) Nogeyama Zoo: Not worth visiting unless you really don't have anything else to combine. Their single only rare species is the crested argus, which is kept off show at this park. The kagus are not worth spending time on when you are in Japan, there are a couple places in Europe where you can easily strike it off your list. If you decide to go anyway, then it is best to combine it with Kawasui Kawasaki Aquarium as was said already. This new aquarium has a whole bunch of rarities, including the only two gollum snakeheads (Aenigmachanna gollum) on public display in an aquarium. This species was only discovered in 2019.
9) Yokohama Hakkeijima Sea Paradise: This place is expensive. Combinable with Zoorasia, like we did. Hakkeijima might not be worth your time or money, but it does have a lovely wall of crabs and other invertebrates that will bump your numbers. The place also has some other rarities like Chaetodon larvatus & Narke japonica. Don't forget to focus on the sharks either, they have multiple Carcharhinus species thrown together in the main tank.
10) Saitama Children’s Zoo: Quokka, of course. The enclosure itself is only open 2-3 hours a day, don't miss it!
11) Tama Zoo: Another lovely park. I recommend spending enough time at the mole house (4 new mammal species for you I'd say) and the insect houses. The park also has Hokkaido mountain hare & two subspecies of Japanese hare. Then there is the crested honey buzzard & Japanese golden eagle that you can't miss. All of these shouldn't be too hard. Don't get your hopes up for seeing the moles inside one of the feeding boxes, even the zookeepers barely see this happening and it only does happen after closing time. Tama Zoo also has adult fireflies on show, at the insect house. Look carefully, I almost missed that little cave myself. Don't forget the yellow-footed rock-wallabies either. After digging a lot, I found out that they belong to the other subspecies than the ones in Europe/America. Last but not least, when you go during the winter I recommend walking past the giant flying squirrel enclosure on your way out when it's dark outside. They come out at this time. We were only lucky when it was that late.
12) Inokashira Park Zoo: Definitely combine this with the Sunshine aquarium and not with Tokyo Sea Life Park. The latter is too big and you will need your time there. Sunshine aquarium is small but got some very interesting species. Their collection of Chaetodon is fairly large, they have Trichiurus japonicus, Sepia kobiensis, etc. In the main tank they have Naru eagle ray, some of the only ones in captivity (besides two other Japanese aquariums). And then there are the mormyrids upstairs. They have 8 species combined, so take as many pictures as you can. The species are not labelled, but I have the list when you need it. Inokashira zoo is perfect for in the morning, you will see a lot of Japanese endemics. Their crested kingfisher died, unfortunately.
13) Tokyo Sea Life Park: Great facility. Indonesian whaler sharks are important here. They have a lot of other rarities as well, many of which are rather small. Go slowly here, one tank at a time. They also have Chaetodon daedalma on show, as well as a large collection of parrotfish. Lovely aquarium.
14) Ueno Zoo: The great slaty woodpecker here is the only one in captivity, but he is very old. He is easy to see. The mammal house is definitely your main target, as it holds a lot of rarities including tarsier & Prince Demidoff's bushbaby. The lights are tricky, so don't count on great photography options. Lidth's jay is another bird you can't miss, it's at the birdhouse near the entrance.
15) Sumida aquarium: Combine it with Ueno if you need to see this place. It's small and only has limited species.
16) Maxell Aqua Park Shinagawa/Shinagawa Aquarium: These two places are tiny and easily combinable. We went to Shinagawa first. Their collection was very disappointing and the park currently doesn't have any species that can be considered unique or very rare. We did manage to find an emperor shrimp and Discordipinna griessingeri but both species can be seen in Europe as well and the first one probably didn't survive anyway. Maxell on the other hand is worth a visit. It has a reef manta ray swimming in the big tank, as well as 3 species of sawfish. This place is the only one in the world to have dwarf sawfish.
As you can see there are a lot of parks in Japan, not all of which are worth visiting. I have stated which places I don't consider going to. But there are some other parks I would like to recommend instead. When staying in Tokyo, Aquamarine Fukushima is actually not that difficult to get to. This place is the only one in the world to keep a ribbon seal. Besides this animal, it has the largest collection of deepsea/arctic fish species I have ever seen. Literally tons of species here cannot be seen in any other aquarium in the world. I hope you find a way to put this park on your list, it won't disappoint. They currently also have sevengill shark, I'm not sure if you have seen it before?
Another aquarium worth looking into is Aqua World Oarai. It holds the largest collection of sharks in the world. They currently have a juvenile tiger shark on show (I missed it, ugh), as well as salamander shark, necklace carpetshark & smooth hammerhead shark.
I know it's far out of reach, but Asa zoo also got the only pair of forest elephants outside Africa. Port Of Nagoya Public Aquarium has emperor penguins. Higashiyama Zoo has over 100 species of killifish & a small Indian civet.
Those are my recommendations. Took me over an hour to write all of this, haha. Good luck with your trip. Feel free to contact me on Facebook (Jo Kuyken), if you have any other questions.
I really appreciate your help, it's awesome.
I understand that it's difficult to understand why I would not travel to Fukushima and Aqua World Oarai in this trip if I am looking for rare animals. But you have to understand that I am not traveling alone and my companions are not zoofreaks: they will travel with me and they will make a great sacrifice, so we will use all the time we have outside the zoos and aquariums to go sightseeing and see everything typical of Japan that we can . That's why I also visit some small parks that allow me to use the rest of the day to do other things.
Thanks to your advice I have removed some centers and added others. Currently, the schedule would be as follows:
Day 1.
Kobe Oji Zoo
Kobe Animal Kingdom
Day 2.
Atoa
Suma Aqualife Park Kobe
Day 3.
Osaka Aquarium
Day 4.
Tennoji Zoo
Day 5.
Toba Aquarium
ISE Sea Paradise
Day 6.
Atagawa Tropical and Alligator Gardenis
IZoo
Day 7.
Zoorasia
Day 8.
Nogeyama Zoological park
Day 9.
Yokohama Hakkeijima Sea Paradise
Kawasui Kawasaki Aquarium
Day 10.
Saitama Children’s Zoo
Day 11.
Tama Zoo
Day 12.
Inokashira Park Zoo
Sunshine Aquarium
Day 13.
Tokyo Sea Life Park
Day 14.
Ueno Zoo
Day 15.
Sumida Aquarium
Day 16.
Maxell Aqua Park Shinagawa
Day 17.
Shinagawa Aquarium
Every day we will do tourism at the end of the zoos and aquariums, so the days will be full of activities even if it doesn't seem like it.
What do you think?