This build is for dd hunting and surprise attack.
Basically you have oustanding DPS with this gunboat but not a great mobility (especially for harugumo). So when you engage make sure it's on your terms.
Your prime target are DDs and some unaware light cruisers.
Use IRF to locate any DDs on your flank get him clean off the game and pop your smoke to avoid too much focus once you're done. Then you can spam some HE to BBs or ship alike that were on said flank. Leave when you can/when smoke disappear and go hunt some other DDs. Stay careful of thje matchup, depending of your first engagment , you might not be able to whistand a second duel.
For light cruiser, you can deal a ton of damage (with AP if broadside) but be careful that they can tear you down really quickly. So you prefer a surprise attack when they're engaging someone else.
As said before the smoke is used to flee. But do not hesitate to use it to spam some HE on heavy cruiser/BBs. As we don't have IFHE on this build you won't be pening a lot but you'll get a good amount of fire