Tatsunori Hara became the 21st manager in NPB history to record 600 victories (600-472-27). He's also just the 4th manager in Giants' history to reach the milestone, behind Shigeru Mizuhara (881-499-29, lifetime 1586-1123-73), Tetsuharu Kawakami (1066-739-61), and Shigeo Nagashima (1034-889-59); and the 3rd active manager behind Senichi Hoshino (962-843-38) and Masataka Nashida (631-563-19, accomplished earlier this year).
Hara also notched his 600th victory in his 1,099th game, good for 8th quickest on the All-time list and third quickest in franchise history (behind Mizuhara's 910 games, Kawakami's 1,025 games, and ahead of Nagashima's 1,188 games).
If I'm not mistaken, Hiromitsu Ochiai is also 1 victory away from 600.
UPDATE 8/21 @ 3:29pm - added additional information.