Yukari heals the person with the lowest HP number. Even if Akihiko is missing half his health and she's only missing 1 point, if her actual total is lower she'll target herself since she has "the lowest hp".
IIRC there's another command that will make her target Akihiko instead in that instance. I think she'll target lowest % on General, but I haven't played the game in a while so don't take my word for it 100%.
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