my flight arrives at 5 am on a Monday
On the supposition that you complete your immigration procedure by 7 am,
you (probably before the peak of the commuters' rush) can get to Asakusa
and then you can take Tobu Limited Express Revaty Aizu
(Asakusa 9:00 -- 11:07 Kizugawa-onsen).
For your two-day trip to Nikko including Kinugawa Onsen,
Tobu Nikko Pass world heritage area (2-day, 2000 yen) may well be suitable.
Showing this pass at a Tobu ticket window,
you can get a 20 percent discount on the Tobu Limited Express surcharge. http://www.tobu.co.jp/foreign/en/pass/twoday.html
In a case
where you don't get back by Day 2 from Nikko to Tokyo
or you plan to make another trip somewhere around Tokyo mainly by JR East,
JR East pass (which covers your rides on JR-Tobu through trains)
may be a better deal.
: Tobu Nikko Pass covers your Tobu bus rides
between Tobu-nikko Station and the world heritage area;
JR East passes are not valid on Tobu bus lines.
Tobu Tourist Information Center Asakusa,
which is on the 1st floor of Asakusa Station, is open from 7:20.
You can purchase there
your Tobu Nikko Pass and Tobu Limited Express ticket. http://www.tobu.co.jp/foreign/en/tourist/
The most direct way for you to get to Asakusa
is to take a Keikyu - Toei Subway through train;
your walking route from the Toei station to the Tobu station
is not straightforward;
there is no pathway to connect directly these two stations.
you can make two quick transfers,
with the help of passenger-friendly signs found here and there,
at Daimon Station
from Toei Subway Asakusa Line to Oedo Line
then at Ueno-okachimachi + Ueno-hirokoji Stations
from Toei Subway Oedo Line to Tokyo Metro Ginza Line.
From Tokyo Metro Asakusa Station,
you can walk through a short pathway to Tobu Asakusa Station;
you have to go up a staircase to the pathway, though.
: 706 yen as IC card fares:
HND International Terminal --[Keikyu + Toei Subway]--
(A-09) Daimon --[Toei Subway]--
Daimon (E-20) --[Toei Subway]--
+ Ueno-hirokoji (G-15) --[Tokyo Metro]-- (G-19) Asakusa.
: 2000 yen on the Tobu Nikko Pass world heritage area.
: 1150 yen (after the discount)
as Tobu Limited Express Revaty surcharge:
Asakusa --[Tobu]-- Kinugawa-onsen.
: 1070 yen (after the discount)
as Tobu Limited Express SPACIA surcharge:
Tobu-nikko | Shimo-imaichi --[Tobu]-- Asakusa.