Originally Posted by GGM Babygoat

There are two trains actually (Keisei, Monorail) that both have stops at T3 and T1/T2. They’re just both landside. HND isn’t really designed for international transfers. It’s for those connecting to/from Japan. NRT is where most of the I-I transfers go.

Not sure I’d choose KUL as the comparison here. The train broke down due to lack of maintenance and last year passengers stuck on the train after it broke down had to walk on the rails to get off. I’ve also used the recent bus instead and I’m glad they have a separate bus for business class, but I wouldn’t say it’s a luxurious experience.