Take the JR Tohoku Shinkansen from Tokyo to Ichinoseki Station (130-150 minutes) and then the JR Tohoku Main Line from Ichinoseki to Hiraizumi (8 minutes). The entire one way trip costs around 12,500 yen and is covered by the Japan Rail Pass and JR East Pass.

Yamabiko trains along the Tohoku Shinkansen travel directly from Tokyo to Ichinoseki Station in about 150 minutes, but you might be able to save about 20 minutes by taking a faster hayate train from Tokyo to Sendai and transfer to a yamabiko train there. Note that seat reservations are mandatory on hayate trains, while yamabiko trains also carry some unreserved seats.
 

Orientation

Hiraizumi's main attractions are quite spread out and best accessed by bus or rental bicycle, although, good walkers could cover them on foot.

The Hiraizumi "Run Run" Loop Bus connects Hiraizumi Station with all the sites of interest in central Hiraizumi. 2-3 times per hour it loops from Hiraizumi Station to Motsuji, Chusonji, Takadachi Giekeido and back to the station. One ride costs 140 yen, while a day pass for unlimited rides is available for 400 yen. Note, however, that the loop bus does not operate during winter (December to mid April).

In addition, regular buses connect Ichinoseki Station via Hiraizumi Station with Chusonji Temple approximately once per hour and around the year. A separate line, the Keisenkaku-Hiraizumi Line provides access from central Hiraizumi to the more remotely located Takkoku no Iwaya 4-6 times per day (no service during winter).

Hiraizumi is also easily explored by bicycle. A rental shop is located at Hiraizumi Station and offers rentals for 500 yen for 2 hours with 200 yen per additional hour, or 1000 yen for the whole day (9:00 to 16:00). The store is not open from December to March, and also closes on rainy days.

A rental car is not necessary for covering Hiraizumi's central attractions, but can be convenient when also visiting more outlying attractions such as Takkoku no Iwaya and the Genbikei and Geibikei Gorges. There is no rental car outlet in central Hiraizumi, but most major companies have outlets around Ichinoseki Station.