pressure sting 6A 6B 623AA jc barrier block, and play off of reaction from there. my main plan with haku is to break barrier and do max damage 3 stars or less combos, because haku doesn't benefit from combos with more. with the exception of a 6C shippu.
IB, IB, IB, and IB. also it doesn't take that much meter to dish out 3700+ combos with hakumen. just make every hit count with combos like any thing 236A 623AA or go straight to 623AA if you can. Also, it not about gaining the meter, it's about managing it. the best combos use 3 or less mag and do over 300 damage.
Note: j.C land 6A 6B 623AA is a real block string, and moves the libra a lot, also people get inpatient when they are being pressured by haku since he only has like 2 block stings, they try to jump, backdash, shory, and about any other thing you can think of, since this is his only gattling it can also be combo-ed at any point.
j.C > 5C > 623AA combo
6A > 623AA combo ( i use 6A for tech traps and mix up instead)
6B > 623AA combo
623AA combo