Return to Lutz[edit]
Once you have collected all 8 pieces of Nei equipment, it's time to pass through the Crevice again and visit Esper Mansion. Lutz will be awake and waiting for your return. Upon presenting the Nei equipment to Lutz, he will acknowledge you as the saviors of the system, and the only ones who can defeat Mother Brain once and for all. He will offer to send you to the final destination; a base floating in space above the planet.
Note that you have the option to say "No". If you do, Lutz will fully heal your party's HP and restore your TP. This is a valuable service, as it prevents you from needing to travel all the way back through the Crevice to reach a town and stay at an Inn. If you managed to have Shir steal the Visiphone from the Central Tower in Maseo, you can also save your game right here and be able to pick up from here when you return to the game.
If you choose to say "Yes", Lutz will send you to the base known as "Noah". There is only one means of returning to Dezo when you're on Noah: use the Nei Sword. When you're on Noah, if you use the Nei Sword, you will come right back to Lutz, where he can heal your party (and you can save your progress with the Visiphone.)
Note that you should try to have Rolf reach Level 35 before you attempt Noah, not just for the stat increases, but also for access to Rolf final, and very powerful spell, MEGID. MEGID reduces the HP of every member of your party other than Rolf by half, and delivers that many points in damage to the target. With a party of members at level 30 or above, that adds up to substantial damage if they are at full health. However, in order to make use of this spell, you're going to want Amy in the party as well, so she can cast NASAR, which fully restores the health of every member in your party. By alternating MEGID and NASAR, you can do a lot of damage if you have enough TP to do this repeatedly.
Noah[edit]
This is the final dungeon of the game. Compared to the last few buildings you've explored, it's actually surprisingly simple. You begin at the bottom of the first floor. Your goal is to make your way up to the top. To do that, you'll have to find the right stairs that lead you back and forth between the first floor and the second floor. You'll have to do that a number of times to reach your destination, but you are less likely to get lost in Noah.
Floor 1[edit]
Floor 2[edit]
Boss 1: Dark Force[edit]
When you open the box on Floor 1 (marked by the green exclamation point on the map), you will release Dark Force, the evil entity that attacked Alis one thousand years ago. You will have to defeat Dark Force in order to gain access to Mother Brain. It has a lot of health and it will put up quite a fight, so good strategy will increase your odds of survival.
Dark Force employs two tricks to take down your party. He can unleash an energy that does significant damage to every member of your party. Alternatively, he may curse one member with "Evil" status. This status is random and can have different effects. They may get greedy, or scared, and do nothing for several rounds until they come to their senses after a few rounds. Rarely, they may get inflicted with an Evil status that causes them to attack other members of your party.
Because of this, the fight can go wildly different depending on your luck. Dark Force might curse the same party member over multiple times, giving you plenty of opportunities to attack, or he may inhibit your entire party and wipe them out with devastating energy attacks. Therefore, it is important to do as much damage as you possibly can, as quickly as you can. Establishing good defense is also helpful.
No matter what, Rudo should attack with the Nei Shot unless it makes sense for him to use a Star Mist or Moon Dew. When the battle begins, have someone who is holding the Snow Crown (ideally Anna) use it on the first round to improve your party's resistance to techniques (which is what Dark Force's attacks are considered). Assuming Amy is typically slower than Rolf, have Rolf cast MEGID, and have Amy cast NASAR. This combination should see Rolf drain half of the party's hit points and deliver that in damage to Dark Force. Then Amy's NASAR spell will restore them all back to full health. These are very expensive spells, so you won't be able to cast them very many times, but it should be enough to drop Dark Force's health down tremendously before you need to switch to conventional attacks.
Once your out of TP (or if you don't have MEGID to begin with), Rolf and Anna should join Rudo with regular attacks using the Nei Sword and Nei Slasher respectively. If Amy runs low on TP, have her administer Trimates to whoever has the lowest health, in an effort to stave off death. There will be times when your luck is bad and too many of your party members fall under Dark Force's Evil influence, in which case all you can do is try to wait it out or start over. That is why the Visiphone becomes such an important item at this stage in the game. You can even use it right before you start the fight with Dark Force.
Boss 2: Mother Brain[edit]
Once you clear Dark Force, you may wish to use the Nei Sword to return to Lutz, get healed up, and the return to Noah. After defeating Dark Force, he is gone permanently, you will not need to fight him again. When you're ready, proceed past the point where you fought Dark Force, take the staircase on the right, and make your way to the green exclamation point on Floor 2.
You will have finally reached Mother Brain. She will ask you if you want to fight, and you can say "No" if you wish to prepare before the battle. If you say yes, there is a discussion, and she will ask you to change your mind. If you say "No" to this, the battle will begin.
In truth, Mother Brain is actually slightly easier than Dark Force. It can't possess your party members, it has a little less health, and it doesn't do the same amount of damage. Nevertheless, the fight with Dark Force trained you for this fight. You should employ the exact same strategy against Mother Brain that you used against Dark Force. There's little reason to alter it. If it was successful against Dark Force, it will be successful against Mother Brain.
If you succeed in beating Mother Brain, you will be allowed to advance to the room behind it, and learn the secret behind its construction. This will lead to the conclusion of the story, followed by the end credits. Congratulations on beating this difficult RPG.