From Scratchpad

Snakeman will send you to the obelisk in Nakano. Once you reach the Obelisk, talk to the Innocent at X=20\Y=20. He is the NPC in grey overalls and is wearing a mask. The Innocent is trying to collect data on the obelisk, but wants you to help one of the two nearby Devil Busters in eliminating interferring devils.

You can choose to help either Yamaguchi(DBヤマグチ), the Law character with a sword, or Kanou(DBカノウ), the Chaos character that is carrying a rifle. Depending on who you help, what you have to kill, as well as your alignment will change.

If you decide to help Yamaguchi, you will have to kill ten Gyoukis(ギュウキ) and twenty Azumis(アズミ). Many of these devils can be found in the north-eastern area of Nakano. When you report back to Yamaguchi, you alignment should have slightly to Law.

If you decide to help Kanou, you will have to kill ten Kelpies(ケルピー) and twenty Cocktarices(コカトライス). Many of these devils can be found in the south-eastern area of Nakano. When you report back to Kanou, you alignment should have slightly to Chaos.

Regardless of who you helped, you should see an event movie when you report back to your respective DB. Once your DB regains his composure, he will tell you to check in on the Innocent. Do so, and the Innocent will have you deliver the data he gathered to Snakeman. When you return to Snakeman, he will give you four thousand makka.