The ending of Campus Apocalypse doesn't actually state the condition that's generally assumed to make it a bittersweet ending. And you know what they say about assumptions…
"Shinji," Rei asked as they walked to school, "Why have you not gone to visit Kaworu?"
Shinji stopped in his tracks. Rei stopped with him, tilting her head, but it took Asuka a moment to notice that the two of them had stopped. She turned to look at them. "Come on, you weirdos! We don't have an excuse to be late anymore!"
"Wait, hunting for the cores was an excuse to be late to school?" Shinji asked extremely doubtfully.
"No." Rei said, beginning to walk again. "Our mission was secret, so we had to be treated like the other students if we came to their attention." By coming in to class late, for example.
Wait, no, Shinji realized. That wasn't important. Not only because Misato knew he was staying with Kaji and didn't want him to take after Kaji in any way, shape or form so she definitely wasn't going to allow him to skate out of things and think that was an acceptable way to live his life. When for heaven's sake Shinji lived with Kaji, meaning he knew exactly how many problems came from a person trying to skate out of things when Shinji was often the one stuck dealing with the aftermath of Kaji being Kaji and disappearing on assignments for a week without stocking up on groceries for Shinji first. The last thing he wanted was to pick up bad habits like not thinking before he did things, since that would mean he would still have to deal with this hassle after he moved out and wouldn't even have Kaji to blame it on when it was 6am and there were no clean work shirts.
It also wasn't important anymore because Yggdrasil was safe now, because Kaworu had… Anyway, they weren't hunting angels or cores anymore, so the school administration, or NERV masquerading as the school administration, didn't need to make sure the shemhazai could complete that mission and save the multiverse.
Then there was the fact that Rei had just implied… Shinji had to run for a few seconds to catch up with her. "What do you mean?" he asked.
"That Misato will assign us punishments. She once remarked that she liked the thought of having us stand in the hall holding buckets of water for strength training."
That sounded like Misato, but "What was that about visiting Kaworu?"
"Is your hearing going?" Asuka asked, whirling on him, hands on her hips. She was clearly fed up with him holding slowing the rest of them down. Just like when Shinji became a shemhazai, come to think of it. "You haven't visited that weirdo? No wonder he's been getting mopier! Misato brings him his homework, can you believe it? That's just cruel."
"At least this means he is still able to assist me with my math and Classic Literature classes," Rei said.
"If he can't leave Yggdrasil anymore, then how are you visiting him?"
Both of them stared at him. "The same way we always got to Yggdrasil?" Asuka asked, clearly once again reminded that Shinji was an idiot.
"Have you forgotten the way?" Rei asked. Was that why he wasn't visiting their teammate? "I will take you there after school."
"You were leaving Kaworu to mope because you forgot how to get there and were too embarrassed to ask for directions?!" Asuka demanded.
"I didn't know we could still get there!" Shinji said. "I thought the trouble started when my mother made a way in there, so didn't we need to close it off?"
"That was only the plan when we needed to trap the angels in there again to maintain the tree?" Asuka reminded him archly. "Kaworu isn't going to leave when that means everyone would die and he'd blame himself, the dork, and your mom and your fake dad are welded to each other." Around the tree, so they wouldn't be leaving either. "Sealing it off right away would have been stupid. What if it wasn't enough, and we locked the tree and Kaworu in to die?! We'd only have found out we screwed up when the world ended!" Only an idiot like Shinji would think that was a good idea.
"We can see Kaworu again?"
"Well, I'd better see him again," Asuka said crossly. "I loaned him my iPod and if he doesn't give it back so I'm not beyond bored on the bus to the school trip I'm going to kick his ass."
Her words startled a laugh out of Shinji.
"Hey!" Asuka said, putting her hands on her hips and shaking a finger at him. "Shinji, you should start being more polite to your future stepmother!"
"I think you're getting a little ahead of yourself," Shinji said. "There's no harm in trying, but…" Even if Kaji was ever going to get married, he was so unorganized and thoughtless that he'd drive Asuka insane in a week.
She just rolled her eyes. "I'm not listening to what you think about romance when you seriously thought what, that you and Kaworu were separated forever like you were star-crossed lovers or something?"