Suiko III Geddoe Chapter 1 Aila
Geddoe's Chapter 1 should be the last one you do. Geddoe usually has a bit of spoilers as he is more of the behind-the-scenes plot character acting as a member of Harmonia. Not to mention, Geddoe's party generally has the harder chapters / boss fights.
Vinay Del Zexay
The party is to pursue the Fire Bringer story, which started in Iksay (Grasslands). Talk to the villagers of Vinay Del Zexay, and be sure to use your potch on sharpening your party's weapons.
Zexen Forest
Just walk east through the forest. The enemies should not provide much resistance.
Yaza Plains
There are two different routes to take in Yaza Plains, but for now just go straight north.
Great Hollow
Geddoe knows how to talk to these lizards. Shiba lightens up once Geddoe speaks with him.
The main area of the Great Hollow is huge. You can explore later, just follow to the path up and then to the chief. Speak to the guard outside for a Sunbeam Rune.
Geddoe's meeting with Chief Zepon is brief but he understands the main idea regarding the Fire Bringer. Afterwards, go west and talk to the soldier for Old Book Volume 3. Then enter that room, the training center. You won't have much in terms of ability points, but you may as well use what you have. Check out the Armor Shop / Weapon Shop if you want, but you are likely low on funds unless you abused the Lottery system already.
East of the armor shop are three lizards speaking about some suspicious activity. Follow the lizards even though they tell you not to. Just as you begin to follow, the lizards stop and fight you. They have a high attack, but are slow and you should be able to gang up on them slowly. After 3 turns, the battle stops. Shiba joins.
Return back to the training center, as Shiba has a ton of ability points you should use up. Back to the tunnel, and pass through. You will come to another lizard, who runs in the far door. Follow him. Soon you will be outside.
Zexen knights have some lizards down. Battle begins against Chris and five Zexen Knights. Again, unless you abused the Lottery System, it is highly unlikely you will win this battle. Chris will cast Breath of Ice and that should take off about 200 on everyone. A great reward is yours if you win, but don't expect to. The zexen knights flee, but head back inside. Strangely enough, the knights make no noise as they retreat.
Return to where you met with Chief Zepon. Turns out the enemy got Chief Zepon. Geddoe suggests seeing Chief Lucia now of Karaya.
Karaya Village
Aila and four Karayan Fighters greet you at the entrance. Just survive a few rounds and the fighting will stop. Aila just uses physical attacks but if you don't use unites, this group can overwhelm you a bit.
Jimba comes up to you after the fight and stops Aila. Go to the northeast hut for another scene with Geddoe and the chief.
Ace and Joker go off. Head towards the entrance to see Aila and a weird, blue-clad woman. She says the village is going to be burnt down. Aila just chases her down and Joker / Ace choose to follow. Save and rest up before doing so.
Plain Amur
Go to the save point, then head north to see Aila. She then runs off again.
Back in the village, Jimba talks with Geddoe about the Fire Bringer bandits.Combined with the assassination of the Lizard Chief Zepon, things are definitely strange around the Grasslands. The conversation is then interrupted.
Back to Plain Amur, as Aila finds Sarah. However two strange figures teleport in, a guy in black and a robed man. Joker and Ace take Aila and run away. Save your game and go towards the fire in the village.
Karaya Village
Chaos ensues at the village. Queen and Geddoe are together still. If you wish to fight you can choose "I have an inkling". You will be going up against Borus and two Zexen Knights on horses. First of all, hopefully Queen and Geddoe are fully healed to even have a chance. You will need to get off a Soaring Bolt from Geddoe, so hopefully you had a chance to upgrade his Lightning Magic and the other part of the equation is Queen dodging an attack or two from the Zexen Knights. Otherwise she'll get slaughtered and Borus and friends will move onto Geddoe. Whoever wins will gain a ton of experience points. Geddoe and Queen flee, but meet up with Jacques, Ace, Joker and Aila towards Plain Amur.
A few spots open up. You are to go to Caleria to end the chapter, but first check out Mt Hei Tou.
Mt. Hei-Tou
Go east a few screens, then north. Stick to the northeast until you come to a corpse for Recipe #15. Further north for the BlueMantix. The Blue Mantix can be a tough enemy in the low-mid 20's for levels, which you are likely in. It has a long-range attack, and also an area-based poison attack it loves to use when you have a few melee fighters nearby.
The key for your party is to get off Soaring Bolt, and then other lightning rune attacks with Geddoe. Have Aila provide the healing, and everyone else can just do physical attacks. It may take a while, but you will gain nearly 90,000 Potch, along with a Wall Rune, Blinking Rune, Melon Seeds, Old Book Volume 12, some nice armour and Mega Medicines. A decent haul. Head out of Mt. Hei-Tou. One note about these treasure bosses - they re-spawn if you are using a different character or even with the same character so long as you have a few hours of gameplay. For now, on to Yaza Plains.
Yaza Plains
Instead of going directly south, take the western path a few screens. You can now go to Lake Castle.
Lake Castle
Cecile greets you at the gate. Thomas and friends then come by to explain the free trade system at Lake Castle. Now you can 'recruit' characters, though since you have a full party with Geddoe there is not really a point to recruit a lot of characters. Most are better left for the weaker characters. Still, Geddoe will meet Stars of Destiny along his path that are worth recruiting. Before leaving Lake Castle, bring the Old Book Volume 12 to Eike and dump off some spare items to Muto to clear your inventory.
As you leave Lake Castle, Thomas' flame at the Trinity Sight System will open up. You can pick him next time if you wish.
Brass Castle - left side
Take Yaza Plains' south exit so you can go towards Vinay Del Zexay or Brass Castle. Scott and Waurenhyte are outside Brass Castle left side. Scott wants a few Deer Antlers.
Inside Brass Castle, and go to the Rune Master shop. Jeane is here. Ask her to come to Budehuc Castle - she sets up a Runemaster shop and also can be used as a support member. After Jeane joins the 108 Stars, check out the next door Tutor to level up your Lightning Magic for Geddoe. I also suggest getting Joker a Water Rune (from Vinay Del Zexay) and level up his Water Magic here. The Fire Rune is simply broken in Suikoden III. You will constantly be attacking your own allies with the area-based attacks. Better to have a healer instead of a worthless rune.
Vinay Del Zexay
Buy that Water Rune. Check out the Trader Shop for a Deer Antler. We'll drop this off with Scott a bit later. Sharpen your weapons if they are not at level 7 yet. The officer nearby gives you a Medal Set #1. The Item Shop has Belts of Strength, great accessories for your melee fighters. Last but not least, speak with Dominic at the Armor Shop. Buy the Mole Armor from him. Dominic will appreciate your sense of style, and join you. You now have an Armory at Budehuc Castle.
You will also see Guillaume chasing Shabon here. Speak with Nei and Toppo, then head to the square by the Council Hall. Guillaume and Shabon are here. Stop Guillaume and a duel occurs.
Guillaume is pretty obvious with his Deathblows. He will always say "Deathblow Attack!". Other than that, you may want to be conservative and defend. Guillaume is somewhat powerful and can handle quite a few hits. Nei and Toppo come afterwards. You have the option of telling them about Budehuc but I prefer to recruit these three later with Thomas. Geddoe has a stable 6 characters so there is not a lot of variety.
Brass Castle
Sell the Deer Antlers for 2500 to Scott, and he joins your group.
Great Hollow
Head to the top level to train your attack skills. Then head along clockwise to the trade shop. Buy a Crystal Ball here, then speak with the human in blue, red and white. He hands you an Iron Hammer. Give that Iron Hammer to the Lizard Peggy at the Blacksmith shop.
Mt Hei-Tou
Head back to Mt Hei-Tou, and to the spot in the north where BlueMantix is. It will have reappeared, with more treasure. The fight should obviously be much easier now. Just continue to use the Shield Rune level 1 spell early on in battles with Aila to up everyone's attack power essentially, with your allies berserked. Geddoe should of course use Soaring Bolt.
After winning, you will likely gain about 60-70,000 Potch, and some more weapons / items. It should be significantly less valuable than the previous haul, but you will likely get the Medal Set #3 a ? Figurine.
Mountain Path
Far to the southeast on the Suikoden III Map is Caleria and the Mountain Path. Save your game at the beginning part of the mountain.
As you get to the first split, take the east path if you want some Asian Herbs. Probably not worth the walk. Go north to exit. Another long path with a fork at the end in the next area. Go north this time for Medicine. Further east for a save point, and then you'll see a big three-way split with a huge center area. And an area boss ahead.
This is the Twin Snake, with a Right and Left Head. Watch out for this beast's Tri-elemental attack on all members for 100-120 damage. Otherwise it can use physical attacks that take off about the same, but on one character. Also the heads will cast magic, and you can be screwed if it used The Shredding (wind attack) immediately after using the Tri-attack.
As for your strategy, this is one of the toughest mandatory bosses in the game, even for Geddoe's capable party. The goal is to get one of the heads taken out, so that you can avoid the Tri-attacks. Preferably the right head so it won't use Wind Magic on you. Use Great Blessing to heal with Aila, or the first level Shield Rune spell to Berserk everyone. Starting off, use Geddoe's second level magic on the left head and everyone else should attack, except for Joker or Aila if you get hurt. Round 1 you will likely take a tri-attack, but the key is to attack the left head incase it is casting Wind magic. If it gets off the wind magic right away turn 2, you're screwed. Once you take that head out (about 1500-2000 hp), the battle will turn in your favor. It is easy to dodge the physical attacks from the body, and they are only powerful on one ally. The right head uses fire magic but it is weaker and area-based. Definitely a tough battle early on but your rewards are nice in EXP and skill points.
Plus the treasure. You will gain 44000 Potch, with a few Medicines, ? Figurine, ? Statue, Dancing Flames x1, New Casque, Feather Band, New Chain Mail, OldlgtngLeather, New Tunic, Old Silver Robe, Feather Earrings, Winged Boots and a few Antitoxin. Nothing too special but still worth getting of course.
Le Buque is to the north, but you cannot go there so head southeast for Caleria.
Caleria
Lots of stuff in this place, including the frontier defense force's HQ in the back. Check the left though for a blacksmith. There are Tomato Seeds with the other person here. You can sharpen your weapons to level 10, I suggest you do so considering you have a bunch of potch from the BlueMantix (2x) and that Twin Snake. There are some nice things at the rarities armor shop. If you have extra potch, spend it on that.
When you go to the back area by the HQ, the party splits up. Ace goes to give the report, and you regain control. There is a warehouse in the back here, just talk to the northwest guy. Don't worry, it has the same stuff as Muto (somehow). Also, a Bujutsu teacher here. Surely you could use up some of the skill points you gained through Mountain Path.
Duke and friends approach when you get to the Inn. Gau and Nicolas don't talk much but there is Elaine, with her...well, you know. The hunt for the True Fire Rune is about to commence among the border forces. Geddoe Chapter 1 ends, and you can start up Thomas Chapter 1 to finish all the 1's up.