Shibahara beat Miriam Bulgaru 7-5 6-2 and Uchijima overcame Todoni 3-6 7-6(3) 6-2 in two and a half hours in Tokyo to set up a winner-takes-all showdown with Canada on Sunday.
Todoni earned the first break to move ahead 4-2 in the opening set and maintained her advantage to close it out 6-3.
The Romanian also led for much of the second set before Uchijima saved two match points and broke back to force a tiebreak.
Uchijima dominated that and broke Todoni twice in the third set to seal victory.
"I don’t know how I won the match. I am just happy that I was able to pull it off. Of course, the fans helped me a lot," Uchijima said.
Shibahara had put Japan ahead to the delight of a vocal home crowd, pouncing at 6-5 to claim the first set and breaking Bulgaru twice in the second.
"I was nervous in the beginning. I think overall I played well," Shibahara said. "It (the crowd) helps me so much, I love it when they’re loud. I really kept pressing and being aggressive."