Resin composition and fluidity improvement method

A method of improving the fluidity of a polyamide-series resin, comprising:

• combining a compound represented by the following formula (1),
• wherein R1 represents a hydrocarbon group bonded to any substitutable position on either benzene ring of the fluorene ring, k denotes an integer of 0 to 8,
• R2a, R2b, R2c, and R2d independently represent a hydrogen atom or a hydrocarbon group,
• R3a and R3b independently represent a hydrogen atom or a hydrocarbon group, and
• X1a and X1b independently represent a group defined in the following formula (X1):
• wherein R4 and R5 independently represent a hydrogen atom or a hydrocarbon group;
• or R4 and R5 bond together to form a heterocyclic ring containing the nitrogen atom adjacent to R4 and R5,
• with a polyamide-series resin,
• to obtain a resin composition comprising the polyamide-series resin having improved fluidity.