Northern Kyushu 5D4N in itinerary

Hello everyone, much need your advice for the 5 Days trip to Kyushu
Day 1 Arrive at Hakata 13:15
Day 5 Depart from Hakata 14:15
To do list:
Mount Aso, Yufuin Onsen (stay overnight), 99 islands

Anyone can suggest the best route & time schedule for me?

Thank you!!

99 Islands needs a car.
Aso-san needs car or bus.

I don't then 3 full days full is enough/realistic.

Can you drive in Japan? Will you use public transport?

Day 1 - Drive to Yufuin. Approx 90 minutes.
Day 2 - Yufuin.
Day 3 - Drive to Aso-san. Approx 60 mins. Aso-san. Drive to 99 Islands. Approx 180 mins.
Day 4 - 99 Islands.
Day 5 - Drive back to Fukuoka. Approx 90 mins.

I think I made it work with public transport.

D1 - train to sasebo 2 hrs
D2 - 99 islands tour
D3 - train to Kumamoto via Kurume 3 hrs
D4 - bus to Aso-san 1.5 has, bus to Yufuin 1.5 has
D5 - train/bus back to Fukuoka 2 hrs

D1 - train to Yufuin 2 hrs
D2 - Yufuin
D3 - bus to Aso 1.5 hrs, bus to kumamoto 1.5 hrs
D4 - train to sasebo 3 hrs
D5 - train to Fukuoka 2 has

First one has full day at 99 Islands and only sleep and morning in Yufuin. Half day in Kumamoto.

Second on had full day in Yufuin. Half day 99 islands.

D1 - To Yufuin, arrive late
D2 - Yufuin full day
D3 - Aso day trip, bus/car
D4 - To Sasebo 3.5/4.0 hrs travel, half day 99 Islands
D5 - To Fukuoka

D1 - To Sasebo, arrive late
D2 - 99 islands full day
D3 - To Yufuin 3.5/4.0 hrs travel, half day Yufuin
D4 - Aso day trip, bus/car
D5 - To Fukuoka

These look better fine tuned. 2 nights both in Sasebo and Yufuin.

Just choose between full and half days between 99 Islands and Yufuin.

Day 5 you don't need an early departure, so the second itinerary might be better to have a slow morning in Yufuin.

Thank you for your advice, unfortunately I don�ft drive so the trip will be by train/bus

May I check is it possible to run the itinerary as below?

D1: land at 13:50 in Hakata - have lunch and redeem JR - Kumamoto overnight
D2: the earliest train - bus to Mount Aso - Bus (time 14:10) to Yufuin - Yufuin overnight (would like to have dinner at ryokan)
D3: Yufuin breakfast & walk - Fukuoka overnight
D4: Hakata - 99 islands - Hakata
D5: Departure

My must visit is Yufuin and Mount Aso, if is too rush I will not go 99 islands, any alternative recommendations if not going 99 islands?

Thank you again!

You don't have to drive, though it certainly makes it a lot easier and convenient, especially around Aso. You also didn't mention when you plan to travel. For Aso, I hope you are aware that currently you cannot get closer than 1 km from the crater rim. There are some other very good places in the region (Nabegataki Falls, Daikanbo Lookout, Yamabuki Springhead, Kikuchi Gorge, Kuju Flower Park etc) but again, if you don't drive, or at least join a bus tour, it is not really in the cards. Both Yufuin and the Sasebo port are easily reached by train, but given the time on the trains, just taking the island cruise seems a bit of a waste. It's totally worth it, but there is more there - at least find somewhere to try a Sasebo burger. They are very popular in the area. There are also a number of excellent lookout points over the bay if the weather is good, but by car would be ideal.... a taxi could do it for some, but that would still get very pricey. Maybe you could also see Huis Ten Bosch along the way?

Thanks Ken for your recommendation all those spots by car even those I have mentioned I DO NOT drive. And I don�ft really interested a man-made theme park.

I understand. It's up to you to decide if it's still worth going to Aso. You also asked about alternatives, and the first one that comes to mind is Nagasaki - it is a lovely city, and it has a long history with unique Chinese and Dutch influences. Fukuoka City certainly has a number of sights too, like the Nanzoin Temple just outside the city, as well as some nice parks.
https://goo.gl/Q843Bg
There is also Beppu, near Yufuin. It also has some good hot springs, and its Hells Tour. In Oita City too is the Takasakiyama Monkey Park, one of the better ones in the country, plus Umitamago Aquarium, and while it's not the best in Japan, is still pretty good.

Have you researched the tours and ferries for 99 islands. Pretty infrequent. I really don't think you wanna day trip it from Fukuoka and add 4-5 hours return travel time.