Tanegashima via Ferry

Taking the ferry to get to Tanegashima is a slower but definitely more relaxing way to get to the island. You can take the ferry from Osaka to Kagoshima and then take another ferry to Tanegashima. There is no direct ferry from Osaka to Tanegashima.
From Osaka to Kagoshima (Shibushi)

The ferry leaves from the Osaka Nanko Kamome Ferry Terminal and travels to the Shibushi Port in Kagoshima. Then in order to continue via ferry you need to either drive, or take a bus, or a train, to the other side of Kagoshima prefecture to take the ferry to Tanegashima. Pretty inconvenient really but the only choice if you want to travel only via ferry or if you plan to bring your own car.

The following prices are typical:

Price: 15,000 yen - 31,000 yen (tourist - deluxe)

The following was the ferry schedule as of July 2014:
From Osaka to Kagoshima
  Osaka Nanko Kamome Ferry Terminal Departure Kagoshima Shibushi Port Arrival
Monday - Friday 17:55 pm 8:55 am (next morning)
Saturday 17:55 pm 9:40 am (next morning)
Sunday 17:00 pm 8:55 am (next morning)
From Kagoshima to Osaka
  Kagoshima Shibushi Port Departure Osaka Nanko Kamome Ferry Terminal Arrival
Monday - Friday 17:55 pm 7:40 am (next morning)
Saturday 18:30 pm 8:50 am (next morning)
Sunday 17:00 pm 7:40 am (next morning)
 
Osaka Nanko Kamome Ferry Terminal Map Kagoshima Shibushi Port Map
 
Additional Notes
The buffet was available for breakfast from 6:00 am - 7:00 am and for dinner from 18:00 pm - 20:00 pm but be sure to check the times as they do change. The food was average but overall pretty good. A mix of Japanese and western style cuisine there should be something for everyone. The price was about 1500 yen for the dinner buffet for an adult.

The public bath was available in the morning and evening. Again be sure to check the times when you arrive. This is a jacuzzi style bath. Shampoo and body soap were supplied. Be sure to bring your own wash towel and drying towel.
From Kagoshima to Tanegashima

Basically if you bring your own car then you need to take the ferry Hibiscus. If you are traveling without a vehicle then you can take the Hibiscus, which is the cheapest option, or you can take one of the hydrofoils.

The following prices are typical:

Price Hibiscus: 3,500 yen (passenger - one way)
Price Hibiscus: 12,200 yen and up (car - price depends on length)
Price Hibiscus: 2,300 yen (bicycle)

The following was the ferry schedule as of July 2014:

Note: Hydrofoil information to follow.
 
From Kagoshima to Tanegashima
  Kagoshima Port (Nanatsujima) Departure Tanegashima (Nishinoomote Port) Arrival
Daily 18:00 pm 21:40 pm
From Tanegashima to Kagoshima
  Tanegashima (Nishinoomote Port) Departure Kagoshima Port (Nanatsujima) Arrival
Daily 11:00 am 14:40 pm
 
Kagoshima Port (Nanatsujima) Map Tanegashima (Nishinoomote Port) Map
Map not working Map not working
 
Additional Notes
The ferry Hibiscus is absolutely a no frills trip. The only food for purchase is cup ramen and drinks all from vending machines. This is a three and a half hour trip....be sure to pack a lunch. There is a TV in the group passenger room albeit Japanese programs and their choice of course.

Note: Be sure not to be on deck when the ferry departs and arrives as the horn sound from the speakers is deafening....scared the shit out of our son.
Additional Information