Read about main endings of the game. It focuses on the normal route instead of the hikkiomori route.
Please note that you have to confront Basil during the sleepover to reach this point.
You should be in the recital room during the finale of the game. Play the violin and enjoy the ensuing cut scene. You will go to the white space to confront Omori. Fight him until he makes you afraid. At this point you can either let him kill you or keep trying to beat him until he kills you.
Choose to continue. Enjoy the cut scene. You will wake up in a room. Leave the room and head down the hallway. You will see your friends and Basil. Both groups will head in opposite directions. Follow Basil to another room and head inside for the ending.
Please note that following the children leads to a dead end. It won’t hurt you if you check it out.
You have to water Basil’s plants 3 times to unlock the secret ending. It plays after the credits on the good ending. I’d water it over the several days to be safe. Keep in mind that watering them gives you bonuses.
Do not continue. Enjoy the ensuing cut scene and events. You will eventually wake up on the roof. Jump off to unlock the ending.
You a number of options on what you can do here. A lot or little can happen depending on your choices here.
To unlock the other ending achievement. Go straight home after sleeping over at Basil’s house. Do not kill yourself. Watch the ending credits in its entirety.
You should be at Basil’s house having a sleep over with your friend’s. You can go to sleep OR skip out and head on home. Check below (*) to see what you could do at home. If you go to sleep. You will wake up while everyone is still asleep. You can either go back to sleep OR go home. The third option is to confront him except this will lead to the good ending.
If you go back to sleep. When you wake up. You will be the only one in the room. You can skip the next part and go straight home. If you go look for everyone. You will find them all in the hallway near Basil’s room. Basil’s is in his room. You can do nothing else other than talk to everyone before heading home.
Once you have gotten home. You now have two options of either grabbing the knife in the kitchen or heading straight to your room.
Go to bed to enter the white space. The room is now fairly plain now leaving you only one option of stabbing yourself to «wake» yourself up. You have only two variations of an ending you can reach in the morning. Either it ends with either both Basil and yourself dead; or only Basil dead and your character moving away.
Again, to unlock the other ending achievement. You do not kill yourself and move away.