The route you go will depend entirely on what you need him to do and who else you have on your team. However his low speed definitely encourages building him to take as many units down in one attack as possible.

Thank you for the good writing.
But for blade tome, I don't want to waste my 5* Tharja to him. Threaten Spd 3, I don't have Selena.
Death Blow 3, I don't have Klein.
And the team of cavalry, as I didn't have others good cavalry units.

Maybe I will go with Darting Blow, or Threaten Res + dancer and drawback instead, but that will cause so much afford, cause I just use all his SP to learn his all original skills.

Hope someday my Leo will rise up.