Hikifune and main 9th skill

Zento-Hazashi

Main skill affects her buff so it won't stack yes

but if you are going to use 9th skill, have Hiki attack first as usual tho, it only lasts 1 round as the attack buff, so once your main does his skill or normal attack, that buff will go as natural and his new buff will kick in (the 15% attack increase by 9th skill) ^^