I don't usually recommend Seishun 18 kippu for foreign tourists as JR Pass has excellent value if planned well.
That being said, I advise you to travel like this:
15 - Kansai Airport to Osaka
16 - Osaka
17 - Osaka
18 - Kyoto(daytrip)
19 - Kyoto(daytrip)
20 - Nara(daytrip)
21 - Yoshino(daytrip)
22 - Osaka to Ise-shima(to Nagoya, even Night train to Tokyo)
23 - (to Nagoya) to or around Tokyo
24-26 - Explore Tokyo and Yokohama
27 - leave Tokyo at 11.55pm.
Kintetsu Rail Pass should be used during Dec 18-22 or 19-23(till Nagoya)
Seishun 18 Kippu should be used from 23 - 27.
Moonlight Nagara night train from Nagoya to Tokyo is popular and sometimes booked out. In that case, it takes 7 hours to travel from Nagoya to Tokyo during daytime.