The Coast of Minoz is a large area which splits to two paths, each containing their own Gathering points and treasure chests. (Refer to the map above to learn their exact location) While exploring the area, Miki will give a remark about a strange, creepy sound emanating somewhere in the coast. When you're near the part of the coast where the two paths converge, you'll spot the abnormally large gerel or slime monster from a distance. Make sure to heal up with your berries before engaging it.
Boss: Discord Gerel
This boss is basically the larger and tougher version of the slime monsters you've been wiping out earlier. It has the same attacks (though more powerful) as an ordinary gerel and comes along with three ordinary ones. Take out the smaller gerels first then let Miki do the healing and ranged attack. If she can't keep up with the healing for some reason, take control of her and manually cast healing via the Signeturgy battle menu.
Shortly after, Victor will arrive to lend a hand. He's basically a tank so he'll draw the aggro. Miki will do a great job in healing the attackers, either when controlled by the AI or the player. The damage output will be increased as well, thanks to Victor so this corrupted gerel will be destroyed shortly after.
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After the battle, you'll have a conversation with him. He will also agree to escort you to the next settlement. While you have him as a third party member, you can explore the other portions of the Coast of Minoz with ease. Use this chance to collect the remaining items in the area and maybe earn a few levels and some more SP for your roles and specialties. Once you're done, continue heading to the northeast to reach the town of Myiddok.