should I buy 7 days JR pass

Hi there!

Yes the JR Pass would offer you amazing value. Below is a little list of ticket prices you'd pay without the pass.

Kyoto - Nara (return) ¥ 1,380
Kyoto - Hiroshima ¥ 10,990
Hiroshima - Miyajima (return) ¥ 1,140
Hiroshima - Tokyo ¥ 18,050
Tokyo - Nikko ¥ 5,630
Nikko - Tokyo ¥ 5,630
Tokyo - Hakone (Odawara) ¥ 3,840
Odawara - JR-Namba ¥ 12,470

For a total of ¥ 59,130 or ¥ 30,830 in savings As the 7 day JR Pass is ¥ 28,300. So I would certainly use a JR Pass for your travel.

Although the difference is small, I think that activating your JR Pass on D4 would allow you to make best use of it.

Hope this helps!
Daniel

Thanks Daniel.
I shall go for JR pass and activate that on D4.
Thanks again.