Getting to Kamikochi by highway bus from Tokyo.
Direct bus service or via Matsumoto/Hirayu

1. Shinjuku → Kamikochi (direct bus)

* Fares for overnight buses with 3-row-seat cost 1,800 JPY in addition to the normal fares for both adults and children.

2. Shinjuku → Matsumoto → Kamikochi (via Matsumoto)

For this route, take the highway bus from Shinjuku bound for the Matsumoto Bus Terminal, get off at the Matsumoto Interchange bus stop, take the Kamikochi Line railway, and then a local bus.
We recommend you stay a night in Matsumoto, a city nestled in the mountains and the gateway to the Northern Japan Alps, before making your way to Kamikochi the next morning.
The frequency of highway buses running between Shinjuku and Matsumoto is also a key point.
24 round-trip highway bus services operate daily between Shinjuku and Matsumoto.

See here for more details.

3. Shinjuku → Hirayu → Kamikochi (via Hirayu Bus Terminal (Hirayu Onsen))

For this route, take the highway bus from Shinjuku bound for Hida Takayama, get off at the Hirayu Bus Terminal, and change to a local bus heading for Kamikochi.
After exploring Kamikochi, we recommend you take the bus back to the Hirayu Bus Terminal and stay a night in either Hirayu Onsen or Fukuji Onsen (part of the Okuhida Onsengo Hot Springs), where you can soothe your weary body in the hot springs.
4~5 round-trip highway bus services operate daily between Shinjuku and Hirayu.

See here for more details.