So quite a few people have crossed Kratos's path in his time at Landel's Institute. Most of them were just that: people he's come across one time or another. But there's a few that stand out.
At the Institute
per_ardua: What to say about The Professor. In the beginning, both were fairly professional (read: "civil") toward one another, and events have either shifted that relationship toward something closer to friendship or toward thinly-veiled animosity. Overall, though, they're comfortable enough with each other that one has no problem initiating a random conversation with the other. Call it a "tentative alliance".
Surprisingly enough, Kratos has shared with Raine a number of things that he would probably never tell anyone else in the world--mostly because she is very, very persistent. But it also could be said that within Landel's, Kratos has no one else to turn to whenever he needs to vent (which happens often enough, oddly), and in a place where maintaining sanity is key, one can't afford to be picky. And she's slapped him. He's found that Raine is indeed good when catharsis is needed, although he'll never admit it. Ever.
There is a running tally between the muns of who causes the other more grief, and right now Raine has the most strikes against her.
akarusa: Hokuto and Kratos have been stuck together often in recent times, mostly through Arts and Crafts activities. He doesn't approve of her fashion sense, or of the way that she seems determined to get him to talk about himself, but she's a kid and he's a parent, so he'll watch out for her.
repelling aka "Sub-Son": [copypasta from the relationship meme] So Ishida is the...Kratos has lost count of how many Arts and Crafts Teenagers he's "chaperoned" (even though there can't have been more than five or so), but so far, he finds this one tolerable, if not the most acceptable. Ishida is intelligent, has some fighting ability, and doesn't ask unnecessary questions - all crucial traits necessary for working well with Kratos, especially that last one. Even so, he thinks the boy could stand to learn a lesson in humility; one day, Ishida will run into someone who won't be as...caring perceptive.
There's another matter, and that's Ishida's age. Kratos is fairly disturbed by the idea of relative children dealing with the institute (He thinks more like a dad these days.), regardless of how capable they are, and thus he'll instinctively try to deflect the brunt of the institute's wrath away from them...and mostly toward himself. It isn't readily noticeable - Kratos usually doesn't make his intentions well-known - but it is there, and Ishida is no exception.
Released
for_marian: Surrogate son the first Right off the bat, these two clicked. Maybe it was because Leon saw Kratos as the father figure he never had (just shows you how terrible Leon's father was), or maybe it was because in turn Kratos saw a little too much of himself in Leon. Either way, Kratos counted Leon as the only person in the entire Institute whose company he genuinely enjoyed - and as a loyal friend.
mizuhomaiden: So these two clashed often, and usually it resulted in Kratos getting drenched in some way or another. They generally tried to avoid each other, but one incident where Sheena actually came to him in tears showed Kratos that she didn't completely hate him...
1imited_edition: Raine's lover friend, and someone that Kratos for the most part respected.
divine_judgment: Even though the Chosen of Tethe'alla actually helped his son, Kratos still found Zelos distasteful, and the other typically felt the same way. So there was no love lost between the two, and there probably never will be.
Grudgingly, though, Kratos will admit the boy has some ability. And occasional use.
Other
Lise (
damned_visitors): Oh, Lise. Also known as the devoted (and living) wife of Kurtis Clarke, Kratos's "real" self, and the mother of Kurtis's (also living) teenaged son Nigel, she shows up every so often to check on "Kurtis" and make Kratos's life hell. He's well aware of the fact that she's not Anna--after all, nothing can ever replace the original; Mithos's quest to revive his sister proved that. He's also well aware that she is more than likely an excellently tailored illusion of the Institute's designed to confuse and weaken him.
However. (And this is the word that Kratos hates.)
However. Deep down, buried under tons and tons of rationalization, Kratos has dared to wonder what it would be like if he were to give up and accept the life that Lise offers, and he's found that some shameful part of himself wants it--badly.