There's some choices that don't actually matter for getting an ending, but I've put them there because they make sense for the girl you're pursuing, or just because it was more convenient than writing out all the options. You should try out some different choices, but just keep in mind:

• If you're not aiming for Aiko's route, you can give any answer when she asks you about sports, as long as you fail her quiz.
  
• You can sleep with Nymph up to three times without breaking another romance, as long as you don't sleep with her after you get together with Rei or Yuuki. Just avoid other choices that lower your workability or you'll get the slacker ending.
  
• As long as you get to the choice where you ask someone to be your girlfriend (i.e., don't romance Rei and don't get a bad ending), you can ask Mineko and she'll never reject you~

Also, odd punctuation and grammar is from the game itself, because ¯\_(ツ)_/¯

Drinking devil
Ruined your life over a round of drinks

Make any choices until you get to the bar, then choose:

• Keep at it.
  
• More drinks?

Dark Grave
Cheatings dark grave

Follow the route for Rei's good end, but instead of "Sorry I'm not in the mood," choose:

• Alright, let's do it.
  
• Tennis Courts OR Sandy Beach.

Watery Grave
Cheatings watery grave

Follow the route for Rei's good end, but instead of "Sorry I'm not in the mood," choose:

• Alright, let's do it.
  
• Swimming Pool.

Follow the walkthrough for Yuuki's good end, but instead of "Sorry I'm not in the mood," choose "Alright, let's do it."

Make lazy/irresponsible choices. For example, sleep with Nymph (three times or less), kiss Mineko, don't help Rei, and avoid work.

Here's a guide to get the least workability points possible. (Not all the choices directly affect your workability, but they might lead to other choices that do.)

• I know quite a bit about Basketball actually.
  
• Center
  
• Double Dribble
  
• Where you cover someone
  
• Offer to help.
  
• Don't tell her about Rei
  
• Maybe a little...
  
• Oh, -now- you want my help?
  
• Go for it. (censored) OR let's do this THEN Keep going, she's nearly there. (uncensored)
  
• Check the Rocky Beach.
  
• I'm broke.
  
• Keep at it.
  
• Wow, you're hammered.
  
• Car Park.
  
• Sounds like you really need my help.
  
• Rocky Beach.
  
• Ferris Wheel
  
• I'd rather not.
  
• That sounds like a good idea...
  
• Lies
  
• Kiss her
  
• Sorry I'm not in the mood.
  
• Tennis Courts.
  
• Let her take the lead.

Bad end 6 - Lonely rejection by Yuuki.
Bad end 7 - Lonely rejection by Rei.
Bad end 8 = Lonely Rejection by Sakura
Bad end 9 = Lonely rejection by aiko
Bad End 11 = Demonic Unrequited Love

Ask someone to be your girlfriend when you're not on her route. The easiest way is to follow the walkthrough for Mineko's good end, then save before the final choice and try each option.

Follow the walkthrough for Aiko's good end, but instead of "If you're sure," choose "Thankyou, but it's okay."

Happy End with Yuuki
Enjoy a nice end with Yuuki

• I'm not big on sports.
  
• Let it go.
  
• Tell her about Rei.
  
• Not really.
  
• Hell with it, sure.
  
• My Pleasure.
  
• Check the Indoor Pools.
  
• Sure thing.
  
• Hand over the bag.
  
• Take the Phone.
  
• Let's not drink anymore.
  
• Reception.
  
• I'll see about calling a repairman.
  
• Yuuki may need help.
  
• Pat her on the head.
  
• Reception.
  
• Ferris Wheel.
  
• I'd rather not.
  
• Sorry, no.
  
• Truth.
  
• Especially you.
  
• Start undressing.
  
• Sorry for the wait
  
• Sorry I'm not in the mood.
  
• Tennis Courts.
  
• Keep it up.
  
• Yuuki.

Happy End with Mineko
Have a happy if easy ending

• I'm not big on sports.
  
• Offer to help.
  
• Don't tell her about Rei
  
• Not really.
  
• Oh, -now- you want my help?
  
• It's what Umi needs done.
  
• Check the Indoor Pools.
  
• Sure thing.
  
• Ask to come in.
  
• Hang up on them.
  
• Keep at it.
  
• Wow, you're hammered.
  
• Car Park.
  
• I'll see about calling a repairman.
  
• Yuuki may need help.
  
• Deflect
  
• Reception.
  
• Car Park.
  
• Kiss her.
  
• Lies
  
• Kiss her
  
• Sorry I'm not in the mood.
  
• Sandy Beach.
  
• Mineko.

Happy End with Aiko
Beat Aiko at her own game

• I know quite a bit about Basketball actually.
  
• Center
  
• Double Dribble
  
• Where you cover someone
  
• Offer to help.
  
• Tell her about Rei
  
• Not really.
  
• Hell with it, sure.
  
• Okay just a little. (censored) OR let's do this. THEN Yeah, I think I heard someone. (uncensored)
  
• Check the indoor Pools.
  
• I'm broke.
  
• Take the Phone.
  
• Let's not drink anymore.
  
• Sandy Beach.
  
• I'll see about calling a repairman.
  
• Hell with it, sure.
  
• Not this time, sorry.
  
• Reception.
  
• Sandy Beach.
  
• There are no faults.
  
• Yeah
  
• Seven
  
• Truth.
  
• If you're sure.
  
• Sorry for the wait
  
• Sorry I'm not in the mood.
  
• Sandy Beach.
  
• Topless!
  
• Aiko.

Happy End with Rei
Tame the wild woman that is Rei

• I'm not big on sports.
  
• Let it go.
  
• Tell her about Rei.
  
• Not really.
  
• Hell with it, sure.
  
• It's what Umi needs done.
  
• Check the Indoor Pools.
  
• I'm broke.
  
• Take the Phone.
  
• Let's not drink anymore.
  
• Swimming Pool.
  
• I'll see about calling a repairman.
  
• Yuuki may need help.
  
• Deflect
  
• Hot Springs.
  
• Sandy Beach.
  
• Truth.
  
• I like you most.
  
• Sure.
  
• Sorry for the wait
  
• Sorry I'm not in the mood.
  
• Swimming Pool.

Demon Slave
Enslaved by a Succubus

Sleep with Nymph four times. Requires the choices:

• Maybe a little...
  
• Sounds like you really need my help.
  
• Ferris Wheel.
  
• I'd rather not.
  
• That sounds like a good idea...
  
• Alright, let's do it.

For the other choices, anything should work as long as you don't get Mineko drunk (Bad End 1). For a more detailed walkthrough, check the 100% Achievement Guide.

Become a Merman
Join Minami under the sea

Check the Rocky Beach both times you have the opportunity, then ask Minami to be your girlfriend. For the other choices, anything should work as long as you don't get Mineko drunk (Bad End 1) or decrease your workability too much (Bad End 5). If you want a more detailed walkthrough, check the 100% Achievement Guide.

• I'm interested in sports too.
  
• Offer to help.
  
• Don't tell her about Rei
  
• Maybe a little...
  
• Hell with it, sure.
  
• It's what Umi needs done.
  
• Check the Indoor Pools.
  
• Sure thing.
  
• Ask to come in.
  
• Take the Phone.
  
• Let's not drink anymore.
  
• Reception.
  
• Sounds like you really need my help.
  
• Reception.
  
• Ferris Wheel.
  
• I'd rather not.
  
• That sounds like a good idea...
  
• Lies.
  
• Sorry for the wait
  
• Sorry I'm not in the mood.
  
• Tennis Courts.
  
• Let her take the lead.
  
• Nymph.

Trio of Love
Create a perfect love triangle

• I'm interested in sports too.
  
• Offer to help.
  
• Tell her about Rei.
  
• Not really.
  
• Hell with it, sure.
  
• My Pleasure.
  
• Check the Indoor Pools.
  
• Sure thing.
  
• Hand over the bag.
  
• Take the Phone.
  
• Let's not drink anymore.
  
• Sandy Beach.
  
• I'll see about calling a repairman.
  
• Hell with it, sure.
  
• Lead the way
  
• Hot Springs.
  
• Ferris Wheel.
  
• Sounds like a plan to me.
  
• Lies.
  
• If you're sure.
  
• Agree with Aiko. OR Agree with Sakura. (uncensored)
  
• Sorry for the wait
  
• Sorry I'm not in the mood.
  
• Swimming Pool.
  
• Aiko.

Even though this is a threesome end with Sakura, asking Sakura instead of Aiko will still get you rejected =(