宿借り, 宿借: a hermit crab

角川: a surname

独自: independent / 独自: unique

独自: being original / 独自: uniqueness

sound of heartbeat

throbbingly, such as with a throbbing heart

(onomatopoeia, often as どかんと) with force or vigor, producing a loud sound; with a bang or thump / (onomatopoeia, often as どかんと) with force or vigor, in great amounts

not necessary to; don't have to

Expresses gratitude or relief for something that happened in the past, a choice made, etc.

If only ~