There are two Keikyu Inn hotels near HND. Be sure to check which one you are staying at:
KEIKYU EX INN HANEDA - a short walk to the West of Tenkubashi station.
KEIKYU EX INN HANEDA INNOVATION CITY - about the same distance to the East of Tenkubashi station.
Tenkubashi station is one stop from T3 on the monorail or the Keikyu line. Both hotels also offer a free shuttle bus. Both hotels offer the following warning on their websites: Please be careful not to confuse it with other nearby "Keikyu EX Inn"! but I am sure that the reception staff often have to deal with customers who walked through the rain to get to the wrong hotel and then walked some more to get to the right one.

As CPH stated, the bus is probably a more comfortable option than taking a Keikyu Airport Express train from NRT.
The Airport Express train is cheap. It requires no changes and it stops at Tenkubashi. Those are the "plus" points, but it is an irritating journey with around 45 stops by my estimate. If you choose to go that route, go to the Keisei platform and look for a train with the destination Haneda Airport. Aim to sit at the end of a bench and lie your luggage on its side (so that it doesn't roll around) in the gap between the bench and the door. Set your alarm to wake you up before Tenkubashi and settle in for a tedious ride.