Instructions
Dive right in! Oichi is one of the initially available characters, so there's no need to unlock her.
Walk the walk. Oichi may have a strange way of running, but she is right behind Hanzo and Kunoichi in terms of speed. Give her the tengu sandals if you think she needs a boost, but don't bother with a horse; she can outrun nearly all of them.
Smile! Nearly all of Oichi's attacks are great crowd clearers. Since her weapon is a ball on a string attached to a toy, she does a lot of spinning moves that send mobs packing.
Boost her power. Oichi may be cute, but she is lacking in the power department. Give her the Power Bracer to help her drive her lessons home a little faster.
Use whatever you like! Both her charge attacks and normal attack string work well in a variety of situations. They are all good for crowd control and moderately effective at staving off enemy officers. Try a good mix and see what works best.
Reach out and touch someone! Oichi's Kendama has one of the best ranges in the game, as one might expect from a ball on a long string. Use it to keep enemies at arm's length.
Use her first charge attack! Unlike most primary charge attacks, Oichi's has a minimal charge time and sends her flying straight through mobs. It is relatively weak and very short compared to most charge attacks, so be careful when charging into big mobs.