This number is a pointer to the place where the animation is installed.
Please import animation, not by hand.
The skill animation extension of FE8J is compatible with the skill animation extension of FE8U.
Therefore, you can use animation of FE8U.
For example, please use the animation released here.
I tried using skill_11 Astra.txt in the Astra (Green) folder in Slanax's SkillAnimation.
In addition, we can convert material for RPG Maker(RPGツクール) by using FEBuilderGBA's magic animation conversion tool.
However, since it decreases to 16 colors, it can not be reproduced much cleanly.
To use this tool, choose Menu -> Tool-> magic animation conversion.
For example, it is the material published on the following blog.
(Note: Redistribution of material is prohibited as this blog material data by license agreement. "Secondary distribution as material is not possible" 素材としての二次配布不可. Please do NOT redistribute it as converted data.)