You decided talking to Kat would be a good option; she's been the matriarch for a while now and has been present during disappearances before. The main part of her job is to protect the tribe's pichu from predators. She saved your life once and afterward, you developed a strong bond with her. Kat was born infertile. For that reason, she was never mated to a buck. Because of her infertility, she became the de facto intermediary between the males and females in the tribe, often keeping the tribe's darker secrets to herself. You ask around and find out she is at your sister's home, consoling her for the loss of her son. You head there.
Outside your sister's burrow is a bounty of flowers and berries - a common practice for pikachu to bring sympathy gifts upon a death, especially a pichu death - and your sister and brother-in-mate outside talking and crying with others. Amongst the small crowd is Kat. Jet was your sister's first son, and she had trouble conceiving this spring. Her heat was dry and she could not get pregnant, so she's without egg thus far. This happens sometimes but is usually temporary; though it could be a sign of infertility to come. But if she is lucky, her heat could start up anytime soon, and they can try again, gods willing.
You, seeing your sister's grief, rush up to her and hug her. You both cry for a minute together over the loss of Jet. You tell her you're so sorry and that it's your fault, but she reassures you it isn't. But you have to keep it brief for the sun is getting late, so you break it off and head over to Kat.
Kat hugs you and tells you how sorry she is. But you stop that conversation there and say, "Listen, Kat. I came to talk about how Jet disappeared."
"Oh yes, of course," she says, "I heard you wanted to investigate further."
"Exactly. Since you were first on the scene, I thought you'd know something."
"I'll be honest with you Lulu, this case seems pretty cut-and-dry."
"Well, anything can help, can you start from the beginning?"
"Okay… it was a nice day out, we went with a larger force than normal, since the vulpix get angsty this time of year as they exhaust the local prey."
"And where was Jet?"
"It was a bit busy, but I distinctly remember Jet moping around. He sat in front of the slowpoke, playing with a rock by himself. I remember because Tay was harassing the slowpoke so I scolded her for it and that's where I remember seeing Jet.
"After that, I'm not sure. Joey - you know how he is - was trying to sneak off, so I went to stop him. While I was telling Joey off, I heard a scream for me. Something like, 'Help Miss Kat; It's eating me." I didn't know who yelled - it was so distressed, I couldn't make out who it belonged to. But we went on high alert and rounded all the pichu in the middle. A few doe went to explore where the sound came from and that's where we found the vulpix, bloody snout and without a pidgey insight - that's what he kept saying, 'it was a pidgey.' My ear it was a pidgey. But the fox is brave - I'll give him that. He wouldn't rat out his friend and stuck to his story, even after the bucks tormented him so. I don't know what else to tell you; did you have any more questions?"
Hmmm… you do. But the thoughts contradict one another, and you don’t have much time; so you'll have to choose.