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I think he'd appreciate it if you told him that 'he's so sympathetic, so cool, I like him so much that I'd like to give him a present. He deserves for being so kind. Though I have no money.'

If you're creative in any way (writing, drawing, music, etc) doing something like that for him would be really lovely, but I think if even all you can do is write a letter then do that.
Like, I don't know about other people, but I find that people usually aren't upfront about how they feel. Sometimes even close friends don't take the time to say out loud 'I love and respect you and you bring so much joy in my life', like, ever.
Splurge a bit on some nice paper and a nice pen and tell your senpai how you feel about him.

I got a letter like that from a roommate in college. She's from Vietnam and was a few years my senior, and we ended up hitting it off. At the end of the year she wrote me a lovely letter and gave me a small windchime that was from her part of the country. I'm literally looking at it right now and it brings back all my fond memories of her.

Even something small will do the same thing for your senpai, I know it. Good luck!

give something that would be useful to his daily lifes so he would use it and remember that it was from you...
maybe something like wristwatch ? with some letter about your feeling and thing

Give him the D... oujinshi.

too much animu

I continue to be both a student and a teacher.

Every time I'm able to share with my teachers how what they teach me helps me and others it has meaning.

How this applies to any relationship is something everyone has to figure out for themselves.

Money can be useful for doing good but many people acquire money by evil means and my teachers would be appalled if I gave them anything acquired by evil means.

try to draw something for him XD

"I'm good at cooking, but he deserves more than something that will last just some minutes"

25 kilos of halva wont be eaten in few minutes.

https://www.youtube.com/watch?v=44kqiL1iwhI&t=0s

Stay communicate with or giving that something senpai always like (Not that one)...

sing a song