Even though Yumi's defense is high, she has low endurance and attack power. She makes up for these, however, with the majority of her moves having freeze abilities. This can stop opponents in their tracks, allowing her to easily gain the upper hand even in the most futile situations. To make up for her various weaknesses, she must take advantage of her chain attacks, Aerial Rave, and Secret Ninja Arts.
Her Frantic Mode makes her even shorter, so use it in conjunction with her Secret Ninja Arts for optimal effect. Deal quick attacks to build up her Ninja Art gauge, then use her Secret Ninja Arts as much as you can. When surrounded, Ice Pillar Fan is the recommended Secret Ninja Art, as it has a large attack range and can rack up a major combo.
Yumi's in-game stats from level 1 to level 50. Please note the numbers listed under the level intervals (anything with a +) does not indicate how much the stat increases between the two levels but rather how much it increases for every 1 level in that range: