IMO the Ratking quest is too short and has no real story to it, so there should be more interactive parts of it, like the Ratking asking for other things ie. asking for Batty Wings and the final quest being to defeat that sewer rat thing.
So basically for the first two quests its just the heads and tails. After that he tells you that he’s tired of eating rattys and decides to go and try eating battys. After eating the batties, he realizes how capable of an adventurer you are and sends you after his competitor for being the Ratking, the Giant sewer rat. If you defeat the sewer rat he acknowledges you are more worthy of being the Ratking then he is and gives you his helmet in respect. Another idea is that the Ratking should be related to the guy who lost the heirloom (I got this idea from a fanfic) so that these two quests will interlock in the sense that after you gave the heirloom back, the guy will tell you that you remind him of his lost brother carl. If you complete the Ratking quest, you should know that the Ratking is called carl, and you can convince him to go back to Nilgarf if you earn his respect. Another prospective idea is that there will be a batking that you can ally with/fight, and it will be your decision who to help. Helping the banking gives you the bat head helm but dosen’t give you the reward from the heirloom guy because you basically killed his brother.
Oh yeah forgot about the rewards
Rewards for completing it for the ratking:
He feels that you are a better ratking and gives you his bucket. This makes all rattys neutral to you unless you attack them, at the expense of having a higher agro range for battys. It gives a int debuff, but gives a str and vit buff. It is better for warriors. (Soulbound)
Rewards for bringing him back to nilgarf:
The guy decides that Carl is more valuable then his heirloom and gives it to you instead, as a necklace. It grants a spell that shoots out a beam from itself and a few extra int at the expense of dex. not soul bound, unlike the other two.
Rewards for helping the batking defeat the ratties:
The batking makes you a member of the cult, giving you a powerful Batmask which decreases monster agro range and increases your str and dex at the cost of vit.
Give me suggestions is the comments I will add it in