It seemed as if Iwai's problems were resolved in GH, but it turns out that he is still struggling with guilt over refusing to enable his mother any longer. Keita is gentle, but firm with him, just like in the original game. This is a sweet story, though it does wrap up a bit too neatly.
Iwai has three endings. The regular endings do not add any extra CGs, but one of them will add an extra entry in the scene list, and you need to fill the list to access the bonus content. (One of the regular endings is totally worthless, lol sorry.)
カラスが好きなんですか？ → (either; only appears if you do NOT have GH data) → 3年の教室へ → そんなことありませんっ → その気持ちが2人に伝わればいいのに
Regular ending 1:
カラスが好きなんですか？ → (either; only appears if you do NOT have GH data) → 3年の教室へ → 岩井さんがそう言うなら
Regular ending 2:
choose the opposite of everything for the love ending, then choose そんなことありませんっ for the 3rd/4th choice
Kawamoto (the art dealer who helped Iwai in GH) calls the school, informing Iwai that he's won a very important prize for one of his paintings. Thing is, the painting was one that Kawamoto decided to exhibit on his own, but more importantly, it's the same prize that Iwai's father won a while back by using one of the paintings he stole from his own son. There's a lot of ~feels~ wrapped up in this for Iwai, and he intends to turn down the prize.
Iwai needs someone who can give kind but firm support
Basically, Iwai is still weighed down by the guilt of hurting his parents - in GH he finally grew a spine and refused to let his mother have any more of his paintings, which she gave to his father so he could pass them off as his own work. It kind of worked out okay because his parents are actually living together now (Iwai's mother is "just" the guy's mistress, but he got divorced after the scandal broke etc) but they haven't talked at all since then.
Kawamoto asks Keita to try and convince Iwai to accept the prize, and Keita asks Kawamoto for his parents' contact information. When he calls, he talks to Iwai's mother, but all she can do is cry and apologize, saying that she doesn't intend to talk to Iwai because he hates her. Keita is surprised because he intended to persuade them to apologize, but it turns out that it's more complicated than he thought. Iwai and his parents have the same worries/feels about each other. Sob.
After this, Keita goes to the art room and they talk. Keita is pretty pushy about it (shades of Yuki ahaha) and while they're in the room, there's an earthquake. It knocks over a bunch of paintings, including one of a happy couple. Turns out, it's a painting Iwai did of his parents. It has a gentle feeling and it's like Iwai put all of his feelings of wanting his parents to be happy into the work. Keita admits to calling his mother, and asks if he can borrow the painting, which Iwai allows. He also convinces Iwai to accept the prize.
Fast forward to the award ceremony. Just before it's time to receive the prize, a bouquet arrives for Iwai with a card attached. It's from both of his parents, congratulating him on the prize. It turns out that Keita sent them the painting along with a letter explaining the situation, and somehow it got through to them. Iwai's father even notes that he wants Iwai to do his best as a painter and surpass him. Sniffle.
it's Iwai, did you expect this to not be the emo route?
Back at the school, the two are talking on the roof. Iwai, who has always been so selfless, tells Keita that he wants to say selfish things sometimes... like wanting to kiss. So they kiss on the roof, ignoring the bell that marks the end of lunchtime.
that rooftop seems to be a pretty popular place for kissing and the like