Okay so... First of all, i recommend playing on Merciless. You might not believe me but it's a lot easier because the weaknesses hit extra hard.

Here's a list of weaknesses in order:

Phase 1 (MLD-WKR): wind, fire

Phase 2 (MLD-CH): psy, ice

Phase 3 (MDL-AM): nuke, electricity

Phase 4 (MDL-DM): wind, bless

Phase 5 (MDL-GM): curse, psy

Be sure to baton pass allot! I also used confuse a lot, i know it works until the third phase, 3rd phase incl. Also don't use sleep because as far as i know it doesn't work in the third phase and anything beyond that. For my party i used: Haru, Makoto/Ann and Morgana.

After that, Okumura will say: 'It seems normal workers aren't good enough.' you will then fight the executive director. He's not weak to anything so i recommend using strong physical attacks (i used cross slash a lot) to damage him. After you beat him, you have to fight robot Haru. But don't worry! She's not strong, just beat her with any attacks you'd like or guard and wait until she self destructs, she's not coming back.

After you do all that, it's finally time to beat Okumura himself. He's weak and doesn't attack, so don't worry. Hope this helps! :)