Hi, welcome to Lamute Gang's Adventure Journal Series.
This is BOOK 5 Guides. This is the last book, I'm so happy that I can write this for y'all.
Let's get started.

1. Otter Island, Day 16

Talk to Pikeo to receive [Croniak] Otter Military Academy Entrance Exam

Hand over the 'Letter of Recommendation for the Otter Military Academy' to Ticirio.

Choose Craorshur > Papu > Thousand Year War

2. Otter Island, Day 39

Same as Book 3, talk to Benns Morio to receive Stoneback Crab Scroll.

Change yourself into Otter Soldier by using 'Gallant Conch Blader Transformation Scroll'

Interact to start stoneback crab training.
Benns Morio will give you a Dumb Stoneback Crab scroll. So in order to complete the quest, you'll need wait for tomorrow (since the stoneback crab training only place once a day)
*or maybe you can form a party with someone that has mediocre stoneback scroll (?)

.....the next day.....

Use Undefeated Crab Knight Transformation Scroll to transform into Undefeated Crab Knight (otter)

3. Otter Island, Day 55

You'll need to do stoneback crab training until day 5 to get Bloodthirsty Stoneback Crab scroll to finish this quest.

once you finished, go to Tamtam Island to complete the quest.

Thank you for joining the Lamute Gang's Adventure Journal Series!

-Fin-

Book 1 : Click here
Book 2 : Click here
Book 3 : Click here

Book 4 : Click here

Book 5 : Click here